# void operator — Immediately Invoked Function Expressions

> When using an immediately-invoked function expression, the function keyword cannot be at the immediate start of the statement, because that would be parsed as a function declaration, and would generate a syntax error when the parentheses representing invocation is reached — if the function is unname

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- Canonical URL: <https://wikikv.com/k/ref-mdn-273d916330744722ae69>
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- Updated: `2026-08-16T09:32:06.395141+00:00`
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## Knowledge

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When using an immediately-invoked function expression, the function keyword cannot be at the immediate start of the statement, because that would be parsed as a function declaration, and would generate a syntax error when the parentheses representing invocation is reached — if the function is unnamed, it would immediately be a syntax error if the function is parsed as a declaration.

In order for the function to be parsed as an expression, the function keyword has to appear at a position that only accepts expressions, not statements. This can be achieved by prefixing the keyword with a unary operator, which only accepts expressions as operands. Function invocation has higher precedence than unary operators, so it will be executed first. Its return value (which is almost always undefined) will be passed to the unary operator and then immediately discarded.

Of all the unary operators, void offers the best semantic, because it clearly signals that the return value of the function invocation should be discarded.

This is a bit longer than wrapping the function expression in parentheses, which has the same effect of forcing the function keyword to be parsed as the start of an expression instead of a statement.

Note that this trick only applies to IIFEs defined with the function keyword. Attempting to use the void operator to avoid parentheses for an arrow function results in a syntax error. Arrow function expressions always require parentheses around them when being called.

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