What is the difference between these two functions/approaches?
I use only jQuery for writing JavaScript code. One thing that confuses me is these two approaches of writing functions,
First approach
vote = function (开发者_如何学JAVAaction,feedbackId,responseDiv)
{
alert('hi');
return feedbackId;
}
Second approach
function vote(action, feedbackId,responseDiv)
{
alert('hi');
return feedbackId;
}
What is the difference between the two and why should one use the first approach or the second approach?
The first is a function expression assigned to the vote
variable, the second is a function declaration.
The main difference is that function statements are evaluated at parse time, they are available before its declaration at runtime.
See also:
- Named function expressions demystified (article)
- Explain JavaScript’s encapsulated anonymous function syntax
function myFunction() {}
...is called a "function declaration".
var myFunction = function() {};
...is called a "function expression".
They're very similar; however:
The function declaration can be declared after it is referenced, whereas the function expression must be declared before it is referenced:
// OK myFunction(); function myFunction() {} // Error myFunction(); var myFunction = function() {};
Since a function expression is a statement, it should be followed by a semi-colon.
See Function constructor vs. function declaration vs. function expression at the Mozilla Developer Centre for more information.
The function declaration syntax cannot be used within a block statement.
Legal:
function a() {
function b() {
}
}
Illegal:
function a() {
if (c) {
function b() {
}
}
}
You can do this though:
function a() {
var b;
if (c) {
b = function() {
};
}
}
The first one is a function expression,
var calculateSum = function(a, b) { return a + b; }
alert(calculateSum(5, 5)); // Alerts 10
The second one is a plain function declaration.
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