dca9e4ec10
- A regular function can have duplicate parameters except in strict mode
or if its parameter list is not "simple" (has a default or rest
parameter)
- An arrow function can never have duplicate parameters
Compared to other engines I opted for more useful syntax error messages
than a generic "duplicate parameter name not allowed in this context":
"use strict"; function test(foo, foo) {}
^
Uncaught exception: [SyntaxError]: Duplicate parameter 'foo' not allowed in strict mode (line: 1, column: 34)
function test(foo, foo = 1) {}
^
Uncaught exception: [SyntaxError]: Duplicate parameter 'foo' not allowed in function with default parameter (line: 1, column: 20)
function test(foo, ...foo) {}
^
Uncaught exception: [SyntaxError]: Duplicate parameter 'foo' not allowed in function with rest parameter (line: 1, column: 23)
(foo, foo) => {}
^
Uncaught exception: [SyntaxError]: Duplicate parameter 'foo' not allowed in arrow function (line: 1, column: 7)
45 lines
1 KiB
JavaScript
45 lines
1 KiB
JavaScript
test("function with duplicate parameter names", () => {
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function foo(bar, _, bar) {
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return bar;
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}
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expect(foo(1, 2, 3)).toBe(3);
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});
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test("syntax errors", () => {
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// Regular function in strict mode
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expect(`
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"use strict";
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function foo(bar, bar) {}
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`).not.toEval();
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// Arrow function in strict mode
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expect(`
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"use strict";
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const foo = (bar, bar) => {};
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`).not.toEval();
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// Arrow function in non-strict mode
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expect(`
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const foo = (bar, bar) => {};
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`).not.toEval();
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// Regular function with rest parameter
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expect(`
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function foo(bar, ...bar) {}
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`).not.toEval();
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// Arrow function with rest parameter
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expect(`
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const foo = (bar, ...bar) => {};
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`).not.toEval();
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// Regular function with default parameter
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expect(`
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function foo(bar, bar = 1) {}
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`).not.toEval();
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// Arrow function with default parameter
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expect(`
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const foo = (bar, bar = 1) => {};
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`).not.toEval();
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});
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