var f1 = () => {
return undefined;
};
var f2 = () => {
};
var a = f1(); // undefined
var b = f2(); // undefined
I know the results but I want to know more in-depth. Is that mean in Javascript functions, no return statement identical to return undefined?
I know the results but I want to know more in-depth. Is that mean in Javascript functions, no
returnstatement identical toreturn undefined?
It is in effect, yes. The specification differentiates between the two, but in pragmatic terms, calling a function that "falls off the end" vs. return; vs. return undefined; all have exactly the same end result in terms of what have the call results in: undefined.
In my answer to the dupetarget (I should have realized!) I explain how the spec differentiates them, but again, it's just a spec distinction, not something you can observe in actual code.
It depends.
For functions who are not used as an instance the default return value is undefined.
For a constructor, called with new, it returns this object as default.
Sources:
If there is no return the return value will be undefined it's basically the same as doing return; (without value) since the function will "return" when it is finised (see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/return for information to return)
If you initialize a function (more like a class) than the returned value will be the instance of this function instead.
undefined.for (...); you can only use it by itself, it does not result in a value. An expression is something that results in a value and can be used as part of a larger expression or statement.