Javascript/Jquery-如何检查函数是否返回任何值？
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Javascript/Jquery-How to check if a function returns any value at all?
提问by seamus
Is there a way to check if a function returns ANY value at all. So for example:
有没有办法检查函数是否返回任何值。例如：
if(loop(value) --returns a value--) {
//do something
}
function loop(param) {
if (param == 'string') {
return 'anything';
}
}
回答by SomeShinyObject
Functions that don't return an object or primitive type return undefined. Check for undefined:
不返回对象或原始类型的函数返回 undefined。检查未定义：
if(typeof loop(param) === 'undefined') {
//do error stuff
}
回答by alex
A function with no returnwill return undefined. You can check for that.
没有的函数return将返回undefined。你可以检查一下。
However, a return undefinedin the function body will also return undefined(obviously).
但是，return undefined函数体中的a也会返回undefined（显然）。
回答by Karl-André Gagnon
You can do this :
你可以这样做 ：
if(loop(param) === undefined){}
That will work everytime with one exception, if your function return undefined, it will enter in the loop. I mean, it return something but it is undefined...
每次都会有一个例外，如果您的函数返回undefined，它将进入循环。我的意思是，它返回一些东西，但它是未定义的......
回答by John Slegers
If you want to do something with the output of your function in the case it returns something, first pass it to a variable and then check if the type of that variable is "undefined".
如果你想对函数的输出做一些事情，以防它返回一些东西，首先将它传递给一个变量，然后检查该变量的类型是否为"undefined".
Demo
演示
testme("I'm a string");
testme(5);
function testme(value) {
var result = loop(value);
if(typeof result !== "undefined") {
console.log("\"" + value + "\" --> \"" + result + "\"");
} else {
console.warn(value + " --> " + value + " is not a string");
}
function loop(param) {
if (typeof param === "string") {
return "anything";
}
}
}