return
The return
statement ends function execution and
specifies a value to be returned to the function caller.
Syntax
return [expression];
expression
-
The expression whose value is to be returned. If omitted,
undefined
is returned instead.
Description
When a return
statement is used in a function body, the execution of the
function is stopped. If specified, a given value is returned to the function caller. For
example, the following function returns the square of its argument, x
,
where x
is a number.
function square(x) {
return x * x;
}
var demo = square(3);
// demo will equal 9
If the value is omitted, undefined
is returned instead.
The following return statements all break the function execution:
return;
return true;
return false;
return x;
return x + y / 3;
Automatic Semicolon Insertion
The return
statement is affected by
automatic semicolon insertion (ASI).
No line terminator is allowed between the return
keyword and the expression.
return
a + b;
is transformed by ASI into:
return;
a + b;
The console will warn "unreachable code after return statement".
Note: Starting with Firefox 40, a warning is shown in the console if
unreachable code is found after a return
statement.
To avoid this problem (to prevent ASI), you could use parentheses:
return (
a + b
);
Examples
Interrupt a function
A function immediately stops at the point where return
is called.
function counter() {
for (var count = 1; ; count++) { // infinite loop
console.log(count + 'A'); // until 5
if (count === 5) {
return;
}
console.log(count + 'B'); // until 4
}
console.log(count + 'C'); // never appears
}
counter();
// Output:
// 1A
// 1B
// 2A
// 2B
// 3A
// 3B
// 4A
// 4B
// 5A
Returning a function
See also the article about Closures.
function magic() {
return function calc(x) { return x * 42; };
}
var answer = magic();
answer(1337); // 56154
Specifications
Specification |
---|
ECMAScript Language Specification # sec-return-statement |
Browser compatibility
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