我什么时候应该在 javascript 中的函数后放一个分号？

Question

My examples:

(First example area is the function assignment with semicolon)

function makeImage() {
var canvas = document.getElementById("tshirtCanvas");
**canvas.onclick = function () {
    window.location = canvas.toDataURL('image/png');
};**
}

vs

window.onload = function() {
    var button = document.getElementById("previewButton");
    button.onclick = previewHandler;


    makeImage();
}

I thought I had the hang of when to use it, and when not to, but I guess I do not. Thanks.

Answer 1

You should put a semi-colon after a function when you use it as a value:

 var fn = function () {};
 blarg.fn = function () {};
 doStuffWith(function () {});

If you're just declaring a named function by itself, you don't need the semicolon:

function doFoo() {}

Note that in the top cases, you don't always have to have a semicolon, but you should put one anyway.

Answer 2

Function expressions get semicolons (normal line ending rules apply). Function declarations do not.

http://javascriptweblog.wordpress.com/2010/07/06/function-declarations-vs-function-expressions/

Answer 3

If you are assigning a function to a property , you should put a semicolon. So you could put a semicolon for the window.onload because you are assigning a function to the onload property of the window. The semicolon isn't required, but I highly recommended you put it to prevent confusion.

window.onload = function() {
    init();
    doSomethingElse();
};

From the MDN Docs.

Answer 4

Your function declaration doesn't need it after. Just if you are calling it.

function doThis(args){
getterMethod(args);
}