noImplicitCoercion
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Summary
Section titled “Summary”- Diagnostic Category:
lint/nursery/noImplicitCoercion - This rule has an unsafe fix.
- The default severity of this rule is information.
- Sources:
- Same as
no-implicit-coercion
- Same as
Description
Section titled “Description”Disallow shorthand type conversions.
JavaScript allows shorthand type conversions by using operators like !!, +, ~, etc.
These shortcuts can make the code harder to read and understand, especially for developers
who are not familiar with these patterns. Using explicit type conversion functions like
Boolean(), Number(), and String() makes the intent clearer and more readable.
This rule reports when values are converted to:
- Boolean using double negation
!!value - Number using unary plus
+value, subtraction from zerovalue - 0, multiplication by onevalue * 1, division by onevalue / 1, or double negation with minus-(-value) - String using concatenation with empty string
value + ""or empty template literalvalue +“ - Check index using bitwise NOT with indexOf
~value.indexOf(item)instead of comparing with -1
Examples
Section titled “Examples”Invalid
Section titled “Invalid”!!foo;code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ !!foo;
│ ^^^^^
2 │
ℹ Unsafe fix: Use Boolean() call instead.
1 │ - !!foo;
1 │ + Boolean(foo);
2 2 │
+foo;code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ +foo;
│ ^^^^
2 │
ℹ Unsafe fix: Use Number() call instead.
1 │ - +foo;
1 │ + Number(foo);
2 2 │
-(-foo);code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ -(-foo);
│ ^^^^^^^
2 │
ℹ Unsafe fix: Use Number() call instead.
1 │ - -(-foo);
1 │ + Number(foo);
2 2 │
foo - 0;code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ foo - 0;
│ ^^^^^^^
2 │
ℹ Unsafe fix: Use Number() call instead.
1 │ - foo·-·0;
1 │ + Number(foo);
2 2 │
foo * 1;code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ foo * 1;
│ ^^^^^^^
2 │
ℹ Unsafe fix: Use Number() call instead.
1 │ - foo·*·1;
1 │ + Number(foo);
2 2 │
foo / 1;code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ foo / 1;
│ ^^^^^^^
2 │
ℹ Unsafe fix: Use Number() call instead.
1 │ - foo·/·1;
1 │ + Number(foo);
2 2 │
"" + foo;code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ "" + foo;
│ ^^^^^^^^
2 │
ℹ Unsafe fix: Use String() call instead.
1 │ - ""·+·foo;
1 │ + String(foo);
2 2 │
foo + "";code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ foo + "";
│ ^^^^^^^^
2 │
ℹ Unsafe fix: Use String() call instead.
1 │ - foo·+·"";
1 │ + String(foo);
2 2 │
`` + foo;code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ “ + foo;
│ ^^^^^^^^
2 │
ℹ Unsafe fix: Use String() call instead.
1 │ - </strong></span><span style="color: Tomato;"><strong>·+·foo;
1 │ + String(foo);
2 2 │
foo += "";code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Implicit type conversion is hard to read and understand.
> 1 │ foo += "";
│ ^^^^^^^^^
2 │
ℹ Unsafe fix: Use String() call instead.
1 │ - foo·+=·"";
1 │ + foo·=·String(foo);
2 2 │
~foo.indexOf(1);code-block.js:1:1 lint/nursery/noImplicitCoercion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Using binary operations instead of comparisons is harder to read and understand.
> 1 │ ~foo.indexOf(1);
│ ^^^^^^^^^^^^^^^
2 │
ℹ Unsafe fix: Compare with -1 instead.
1 │ - ~foo.indexOf(1);
1 │ + (foo.indexOf(1)·!==·-1);
2 2 │
Boolean(foo);Number(foo);String(foo);foo.indexOf(1) !== -1;These are not flagged because they don’t perform type coercion:
!foo;~foo;-foo;+1234;2 * foo;foo + 'bar';How to configure
Section titled “How to configure”{ "linter": { "rules": { "nursery": { "noImplicitCoercion": "error" } } }}