useStringStartsEndsWith

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JavaScript (and super languages)

Summary

Rule available since: v2.4.12
Diagnostic Category: lint/nursery/useStringStartsEndsWith
This rule has an unsafe fix.
The default severity of this rule is information.
This rule belongs to the following domains:
- types
Sources:
- Inspired from @typescript-eslint/prefer-string-starts-ends-with

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "useStringStartsEndsWith": "error"
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      }
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    }
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  }
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}

Description

Prefer String#startsWith() and String#endsWith() over verbose prefix and suffix checks.

This rule detects common string comparisons such as indexing, charAt, indexOf, lastIndexOf, slice, substring, match, and anchored RegExp#test calls when they are being used to check whether a string starts or ends with another string.

The rule uses type information and only reports when the receiver is known to be a string. Array indexing and other non-string receivers are ignored.

Examples

Invalid

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declare const text: string;
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text[0] === "a";

/invalid-index.ts:2:1 lint/nursery/useStringStartsEndsWith  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This index access comparison looks like you’re checking a string prefix.
  
    1 │ declare const text: string;
  > 2 │ text[0] === “a”;
      │ ^^^^^^^^^^^^^^^
    3 │ 
  
  ℹ Using the built-in string method is clearer and easier to read.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use startsWith() instead.
  
    1 1 │   declare const text: string;
    2   │ - text[0]·===·“a”;
      2 │ + text.startsWith(“a”);
    3 3 │

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declare const text: string;
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text.indexOf("foo") === 0;

/invalid-search.ts:2:1 lint/nursery/useStringStartsEndsWith  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This indexOf() comparison looks like you’re checking a string prefix.
  
    1 │ declare const text: string;
  > 2 │ text.indexOf(“foo”) === 0;
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^
    3 │ 
  
  ℹ Using the built-in string method is clearer and easier to read.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use startsWith() instead.
  
    1 1 │   declare const text: string;
    2   │ - text.indexOf(“foo”)·===·0;
      2 │ + text.startsWith(“foo”);
    3 3 │

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declare const text: string;
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/^foo/.test(text);

/invalid-regex.ts:2:1 lint/nursery/useStringStartsEndsWith  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This anchored RegExp#test() call looks like you’re checking a string prefix.
  
    1 │ declare const text: string;
  > 2 │ /^foo/.test(text);
      │ ^^^^^^^^^^^^^^^^^
    3 │ 
  
  ℹ Using the built-in string method is clearer and easier to read.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use startsWith() instead.
  
    1 1 │   declare const text: string;
    2   │ - /^foo/.test(text);
      2 │ + text.startsWith(“foo”);
    3 3 │

Valid

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declare const text: string;
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text.startsWith("foo");
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text.endsWith("bar");

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declare const list: string[];
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list[0] === "a";