Oct 8, 2023 · Oct 1, 2023
diff --git a/packages/eslint-plugin/src/rules/prefer-string-starts-ends-with.ts b/packages/eslint-plugin/src/rules/prefer-string-starts-ends-with.ts
    }

    /**
     * Check if a given node is a negative index expression
     *
     * E.g. `s.slice(- <expr>)`, `s.substring(s.length - <expr>)`
     *
     * @param node The node to check.
     * @param expectedIndexedNode The node which is expected as the receiver of index expression.
     * Returns true if `node` is `-substring.length` or
     * `parentString.length - substring.length`
     */
    functionisNegativeIndexExpression(
    functionisLengthAheadOfEnd(
      node: TSESTree.Node,
      expectedIndexedNode: TSESTree.Node,
      substring: TSESTree.Node,
      parentString: TSESTree.Node,
    ): boolean {
      return (
        (node.type === AST_NODE_TYPES.UnaryExpression &&
          node.operator === '-') ||
          node.operator === '-' &&
          isLengthExpression(node.argument, substring)) ||
        (node.type === AST_NODE_TYPES.BinaryExpression &&
          node.operator === '-' &&
          isLengthExpression(node.left, expectedIndexedNode))
          isLengthExpression(node.left, parentString) &&
          isLengthExpression(node.right, substring))
      );
    }

          return;
        }

        const isEndsWith =
          (callNode.arguments.length === 1 ||
            (callNode.arguments.length === 2 &&
              isLengthExpression(callNode.arguments[1], node.object))) &&
          isNegativeIndexExpression(callNode.arguments[0], node.object);
        const isStartsWith =
          !isEndsWith &&
          callNode.arguments.length === 2 &&
          isNumber(callNode.arguments[0], 0) &&
          !isNegativeIndexExpression(callNode.arguments[1], node.object);
        let isEndsWith = false;
        let isStartsWith = false;
        if (callNode.arguments.length === 1) {
          if (
            // foo.slice(-bar.length) === bar
            // foo.slice(foo.length - bar.length) === bar
            isLengthAheadOfEnd(
              callNode.arguments[0],
              parentNode.right,
              node.object,
            )
          ) {
            isEndsWith = true;
          }
        } else if (callNode.arguments.length === 2) {
          if (
            // foo.slice(0, bar.length) === bar
            isNumber(callNode.arguments[0], 0) &&
            isLengthExpression(callNode.arguments[1], parentNode.right)
          ) {
            isStartsWith = true;
          } else if (
            // foo.slice(foo.length - bar.length, foo.length) === bar
            // foo.slice(foo.length - bar.length, 0) === bar
            // foo.slice(-bar.length, foo.length) === bar
            // foo.slice(-bar.length, 0) === bar
            (isLengthExpression(callNode.arguments[1], node.object) ||
              isNumber(callNode.arguments[1], 0)) &&
            isLengthAheadOfEnd(
              callNode.arguments[0],
              parentNode.right,
              node.object,
            )
          ) {
            isEndsWith = true;
          }
        }

        if (!isStartsWith && !isEndsWith) {
          return;
        }
diff --git a/packages/eslint-plugin/tests/rules/prefer-string-starts-ends-with.test.ts b/packages/eslint-plugin/tests/rules/prefer-string-starts-ends-with.test.ts
        x.endsWith('foo') && x.slice(0, -4) === 'bar'
      }
    `,
    `
      function f(s: string) {
        s.slice(0, length) === needle // the 'length' can be different to 'needle.length'
      }
    `,
    `
      function f(s: string) {
        s.slice(-length) === needle // 'length' can be different
      }
    `,
    `
      function f(s: string) {
        s.slice(0, 3) === needle
      }
    `,
  ]),
  invalid: addOptional([
    // String indexing.
      `,
      errors: [{ messageId: 'preferStartsWith' }],
    },
    {
      code: `
        function f(s: string) {
          s.slice(0, length) === needle // the 'length' can be different to 'needle.length'
        }
      `,
      output: null,
      errors: [{ messageId: 'preferStartsWith' }],
    },
    {
      code: `
        function f(s: string) {
      `,
      errors: [{ messageId: 'preferEndsWith' }],
    },
    {
      code: `
        function f(s: string) {
          s.slice(-length) === needle // 'length' can be different
        }
      `,
      output: null,
      errors: [{ messageId: 'preferEndsWith' }],
    },
    {
      code: `
        function f(s: string) {
Original file line number	Diff line number	Diff line change
Expand Up		@@ -161,23 +161,22 @@ export default createRule({
		}

		/**
		* Check if a given node is a negative index expression
		*
		* E.g. `s.slice(- <expr>)`, `s.substring(s.length - <expr>)`
		*
		* @param node The node to check.
		* @param expectedIndexedNode The node which is expected as the receiver of index expression.
		* Returns true if `node` is `-substring.length` or
		* `parentString.length - substring.length`
		*/
		functionisNegativeIndexExpression(
		functionisLengthAheadOfEnd(
		node: TSESTree.Node,
		expectedIndexedNode: TSESTree.Node,
		substring: TSESTree.Node,
		parentString: TSESTree.Node,
		): boolean {
		return (
		(node.type === AST_NODE_TYPES.UnaryExpression &&
		node.operator === '-') \|\|
		node.operator === '-' &&
		isLengthExpression(node.argument, substring)) \|\|
		(node.type === AST_NODE_TYPES.BinaryExpression &&
		node.operator === '-' &&
		isLengthExpression(node.left, expectedIndexedNode))
		isLengthExpression(node.left, parentString) &&
		isLengthExpression(node.right, substring))
		);
		}

Expand DownExpand Up		@@ -567,16 +566,44 @@ export default createRule({
		return;
		}

		const isEndsWith =
		(callNode.arguments.length === 1 \|\|
		(callNode.arguments.length === 2 &&
		isLengthExpression(callNode.arguments[1], node.object))) &&
		isNegativeIndexExpression(callNode.arguments[0], node.object);
		const isStartsWith =
		!isEndsWith &&
		callNode.arguments.length === 2 &&
		isNumber(callNode.arguments[0], 0) &&
		!isNegativeIndexExpression(callNode.arguments[1], node.object);
		let isEndsWith = false;
		let isStartsWith = false;
		if (callNode.arguments.length === 1) {
		if (
		// foo.slice(-bar.length) === bar
		// foo.slice(foo.length - bar.length) === bar
		isLengthAheadOfEnd(
		callNode.arguments[0],
		parentNode.right,
		node.object,
		)
		) {
		isEndsWith = true;
		}
		} else if (callNode.arguments.length === 2) {
		if (
		// foo.slice(0, bar.length) === bar
		isNumber(callNode.arguments[0], 0) &&
		isLengthExpression(callNode.arguments[1], parentNode.right)
		) {
		isStartsWith = true;
		} else if (
		// foo.slice(foo.length - bar.length, foo.length) === bar
		// foo.slice(foo.length - bar.length, 0) === bar
		// foo.slice(-bar.length, foo.length) === bar
		// foo.slice(-bar.length, 0) === bar
		(isLengthExpression(callNode.arguments[1], node.object) \|\|
		isNumber(callNode.arguments[1], 0)) &&
		isLengthAheadOfEnd(
		callNode.arguments[0],
		parentNode.right,
		node.object,
		)
		) {
		isEndsWith = true;
		}
		}

		if (!isStartsWith && !isEndsWith) {
		return;
		}
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -242,6 +242,21 @@ ruleTester.run('prefer-string-starts-ends-with', rule, {
		x.endsWith('foo') && x.slice(0, -4) === 'bar'
		}
		`,
		`
		function f(s: string) {
		s.slice(0, length) === needle // the 'length' can be different to 'needle.length'
		}
		`,
		`
		function f(s: string) {
		s.slice(-length) === needle // 'length' can be different
		}
		`,
		`
		function f(s: string) {
		s.slice(0, 3) === needle
		}
		`,
		]),
		invalid: addOptional([
		// String indexing.
Expand DownExpand Up		@@ -817,15 +832,6 @@ ruleTester.run('prefer-string-starts-ends-with', rule, {
		`,
		errors: [{ messageId: 'preferStartsWith' }],
		},
		{
		code: `
		function f(s: string) {
		s.slice(0, length) === needle // the 'length' can be different to 'needle.length'
		}
		`,
		output: null,
		errors: [{ messageId: 'preferStartsWith' }],
		},
		{
		code: `
		function f(s: string) {
Expand DownExpand Up		@@ -887,15 +893,6 @@ ruleTester.run('prefer-string-starts-ends-with', rule, {
		`,
		errors: [{ messageId: 'preferEndsWith' }],
		},
		{
		code: `
		function f(s: string) {
		s.slice(-length) === needle // 'length' can be different
		}
		`,
		output: null,
		errors: [{ messageId: 'preferEndsWith' }],
		},
		{
		code: `
		function f(s: string) {
Expand Down