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javascriptfunctioniife

Why can't the infix increment operator (++) be used for an IIFE?

I'm learning javascript and I'm struck at IIFE syntax.

I have understood that to write IIFE we need to make the function as expression and then invoke it.

We can make it as expression by wrapping function in between (). Or prefixing the function keyword with +,-,~,!.

Now for the problem, when I prefix with ++ I'm getting error in the console.

Code:

++function(){console.log("hello")}();

Error:

Uncaught ReferenceError: Invalid left-hand side expression in prefix operation

Why can't I use ++? ++ is a unary operator and I thought it will make the interpreter to think anonymous function as function expression just like +,- etc., did.

Where am I going wrong?

Solution

  • It can't be assigned to

    As the error message says, the function()... is not a valid left-hand side expression, i.e., it cannot be assigned to.

    +, -, ~, ! will cause the expression to be evaluated. On the other hand, the increment operator (++) will cause the expression not only to be evaluated, but also modified, which isn't allowed for this expression.