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Rslint

    prefer-string-slice

    Added in v0.10.1

    Configuration

    rslint.config.ts
    import { defineConfig, unicornPlugin } from '@rslint/core';

export default defineConfig([
  unicornPlugin.configs.recommended,
  {
    rules: {
      'unicorn/prefer-string-slice': 'error',
    },
  },
]);

    Rule Details

    Prefer String#slice() over String#substr() and String#substring().

    substr() is deprecated. substring() clamps negative indices to zero and swaps its arguments when the start is greater than the end. slice() supports negative indices and uses the same indexing convention as Array#slice().

    Examples of incorrect code for this rule:

    const prefix = text.substr(0, 5);
const middle = text.substring(2, 5);

    Examples of correct code for this rule:

    const prefix = text.slice(0, 5);
const middle = text.slice(2, 5);
const suffix = text.slice(-5);

    The rule checks optional calls and optional member access. Computed method names and receivers known to be non-strings are ignored.

    Supported single-character substring() patterns, such as text.substring(index, index + 1), are left unchanged, matching upstream's separation between string slicing and single-character access rules.

    Automatic fixes

    The rule adjusts indices when it can convert the call automatically:

    text.substr(2, 3); // → text.slice(2, 5)
text.substring(5, 2); // → text.slice(2, 5)
text.substring(start); // → text.slice(Math.max(0, start))

    An undefined end retains its meaning of “to the end”; a null end still means zero. Fixes assume .length properties are non-negative. Calls whose arguments cannot be converted, or whose conversion would discard comments or repeat side effects, are reported without an automatic fix.

    Options

    This rule has no options.

    Differences from upstream

    rslint also honors explicit non-string JSDoc receiver types, including array annotations that upstream may ignore without a TypeScript project.

    rslint reports calls without an automatic fix when converting them could read a getter or perform a coercion twice. For example, text.substring(0, options.end) and text.substr(0, +value) are left for manual review. Store the end in a local variable first to make an automatic fix available:

    const end = options.end;
text.substring(0, end);

    Fixes that would introduce a locally shadowed or disabled global such as Math, undefined, or Infinity are also withheld. Rename the conflicting binding to allow the fix. Numeric rewrites that do not need those globals remain available.

    Original Documentation