useObjectSpread

JavaScript (and super languages)

Summary

• Rule available since: v2.0.0
• Diagnostic Category: lint/style/useObjectSpread
• This rule has a safe fix.
• The default severity of this rule is information.
• Sources:
  • Same as prefer-object-spread

How to configure

biome.json

{
  "linter": {
    "rules": {
      "style": {
        "useObjectSpread": "error"
      }
    }
  }
}

Description

Prefer object spread over Object.assign() when constructing new objects.

Object spread syntax is more concise, more readable, and performs better than Object.assign() when creating a new object from existing objects. It also has better TypeScript integration.

Examples

Invalid

Object.assign({}, foo);
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-object-spread">lint/style/useObjectSpread</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Object spread syntax is more concise, readable, and performs better than </span><span style="color: lightgreen;"><strong>Object.assign</strong></span><span style="color: lightgreen;">.</span><br />  <br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>Object.assign(&#123;&#125;, foo);<br />   <strong>   │ </strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>2 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Safe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Replace </span><span style="color: lightgreen;"><strong>Object.assign(&#123;...&#125;, &lt;object&gt;)</strong></span><span style="color: lightgreen;"> with </span><span style="color: lightgreen;"><strong>&#123; ...&lt;object&gt; &#125;</strong></span><span style="color: lightgreen;">.</span><br />  <br />    <strong>1</strong>  <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><strong>O</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>j</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>.</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>i</strong></span><span style="color: Tomato;"><strong>g</strong></span><span style="color: Tomato;"><strong>n</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">&#123;</span><span style="color: Tomato;"><strong>&#125;</strong></span><span style="color: Tomato;"><strong>,</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span><br />      <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">&#123;</span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;"><strong>,</strong></span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span><br />    <strong>2</strong> <strong>2</strong><strong> │ </strong>  <br />  <br /></code></pre>

Object.assign({}, { foo: 'bar' });
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-object-spread">lint/style/useObjectSpread</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Object spread syntax is more concise, readable, and performs better than </span><span style="color: lightgreen;"><strong>Object.assign</strong></span><span style="color: lightgreen;">.</span><br />  <br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>Object.assign(&#123;&#125;, &#123; foo: 'bar' &#125;);<br />   <strong>   │ </strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>2 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Safe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Replace </span><span style="color: lightgreen;"><strong>Object.assign(&#123;...&#125;, &lt;object&gt;)</strong></span><span style="color: lightgreen;"> with </span><span style="color: lightgreen;"><strong>&#123; ...&lt;object&gt; &#125;</strong></span><span style="color: lightgreen;">.</span><br />  <br />    <strong>1</strong>  <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><strong>O</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>j</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>.</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>i</strong></span><span style="color: Tomato;"><strong>g</strong></span><span style="color: Tomato;"><strong>n</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">&#123;</span><span style="color: Tomato;"><strong>&#125;</strong></span><span style="color: Tomato;"><strong>,</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&#123;</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;">:</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">'</span><span style="color: Tomato;">b</span><span style="color: Tomato;">a</span><span style="color: Tomato;">r</span><span style="color: Tomato;">'</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#125;</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span><br />      <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">&#123;</span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">:</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">'</span><span style="color: MediumSeaGreen;">b</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">'</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>,</strong></span><span style="color: MediumSeaGreen;">&#125;</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span><br />    <strong>2</strong> <strong>2</strong><strong> │ </strong>  <br />  <br /></code></pre>

Object.assign({ foo: 'bar' }, baz);
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-object-spread">lint/style/useObjectSpread</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Object spread syntax is more concise, readable, and performs better than </span><span style="color: lightgreen;"><strong>Object.assign</strong></span><span style="color: lightgreen;">.</span><br />  <br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>Object.assign(&#123; foo: 'bar' &#125;, baz);<br />   <strong>   │ </strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>2 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Safe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Replace </span><span style="color: lightgreen;"><strong>Object.assign(&#123;...&#125;, &lt;object&gt;)</strong></span><span style="color: lightgreen;"> with </span><span style="color: lightgreen;"><strong>&#123; ...&lt;object&gt; &#125;</strong></span><span style="color: lightgreen;">.</span><br />  <br />    <strong>1</strong>  <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><strong>O</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>j</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>.</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>i</strong></span><span style="color: Tomato;"><strong>g</strong></span><span style="color: Tomato;"><strong>n</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">&#123;</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;">:</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">'</span><span style="color: Tomato;">b</span><span style="color: Tomato;">a</span><span style="color: Tomato;">r</span><span style="color: Tomato;">'</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>&#125;</strong></span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">b</span><span style="color: Tomato;">a</span><span style="color: Tomato;">z</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span><br />      <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">&#123;</span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">:</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">'</span><span style="color: MediumSeaGreen;">b</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">'</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;">b</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">z</span><span style="color: MediumSeaGreen;"><strong>,</strong></span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span><br />    <strong>2</strong> <strong>2</strong><strong> │ </strong>  <br />  <br /></code></pre>

Object.assign({}, baz, { foo: 'bar' });
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-object-spread">lint/style/useObjectSpread</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Object spread syntax is more concise, readable, and performs better than </span><span style="color: lightgreen;"><strong>Object.assign</strong></span><span style="color: lightgreen;">.</span><br />  <br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>Object.assign(&#123;&#125;, baz, &#123; foo: 'bar' &#125;);<br />   <strong>   │ </strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>2 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Safe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Replace </span><span style="color: lightgreen;"><strong>Object.assign(&#123;...&#125;, &lt;object&gt;)</strong></span><span style="color: lightgreen;"> with </span><span style="color: lightgreen;"><strong>&#123; ...&lt;object&gt; &#125;</strong></span><span style="color: lightgreen;">.</span><br />  <br />    <strong>1</strong>  <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><strong>O</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>j</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>.</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>i</strong></span><span style="color: Tomato;"><strong>g</strong></span><span style="color: Tomato;"><strong>n</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">&#123;</span><span style="color: Tomato;"><strong>&#125;</strong></span><span style="color: Tomato;"><strong>,</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">b</span><span style="color: Tomato;">a</span><span style="color: Tomato;">z</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&#123;</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;">:</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">'</span><span style="color: Tomato;">b</span><span style="color: Tomato;">a</span><span style="color: Tomato;">r</span><span style="color: Tomato;">'</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#125;</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span><br />      <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">&#123;</span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;">b</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">z</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">:</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">'</span><span style="color: MediumSeaGreen;">b</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">'</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>,</strong></span><span style="color: MediumSeaGreen;">&#125;</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span><br />    <strong>2</strong> <strong>2</strong><strong> │ </strong>  <br />  <br /></code></pre>

Valid

({ ...foo });

({ ...baz, foo: 'bar' });

Modifying an existing object is allowed:

Object.assign(foo, { bar: baz });

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