prefer-string-starts-ends-with
Enforce using
String#startsWithandString#endsWithover other equivalent methods of checking substrings.
Extending "plugin:@typescript-eslint/strict" in an ESLint configuration enables this rule.
Some problems reported by this rule are automatically fixable by the --fix ESLint command line option.
This rule requires type information to run.
There are multiple ways to verify if a string starts or ends with a specific string, such as foo.indexOf('bar') === 0.
As of ES2015, the most common way in JavaScript is to use String#startsWith and String#endsWith.
Keeping to those methods consistently helps with code readability.
This rule reports when a string method can be replaced safely with String#startsWith or String#endsWith.
module.exports = {
"rules": {
"@typescript-eslint/prefer-string-starts-ends-with": "warn"
}
};
Examples
- ❌ Incorrect
- ✅ Correct
declare const foo: string;
// starts with
foo[0] === 'b';
foo.charAt(0) === 'b';
foo.indexOf('bar') === 0;
foo.slice(0, 3) === 'bar';
foo.substring(0, 3) === 'bar';
foo.match(/^bar/) != null;
/^bar/.test(foo);
// ends with
foo[foo.length - 1] === 'b';
foo.charAt(foo.length - 1) === 'b';
foo.lastIndexOf('bar') === foo.length - 3;
foo.slice(-3) === 'bar';
foo.substring(foo.length - 3) === 'bar';
foo.match(/bar$/) != null;
/bar$/.test(foo);
declare const foo: string;
// starts with
foo.startsWith('bar');
// ends with
foo.endsWith('bar');
Options
This rule is not configurable.
When Not To Use It
If you don't mind that style, you can turn this rule off safely.