问题
A lot of people say that this is asked too much in the comments, which made me hesitant to ask this, but I still have not found a solution in their answers, mostly because (1) they are typically using jQuery and (2) the questions usually contain technicalities I do not understand.
I have a function with a variable inside. The variable is assigned a function. I'm sure this concept is not exclusive to AJAX, but that is the context I am using it in, if it makes a difference.
function iClick(this)
{
var foo = "I would like to pass this.";
ajax.onreadystatechange = function (foo) { alert(foo); }
}
I want to pass a variable into the function. However, since there is no original function declaration, how do I specify parameters? Can I even do that?
回答1:
Just don't declare that variable as a parameter in your anonymous function, like this:
function iClick(this)
{
var foo = "I would like to pass this.";
ajax.onreadystatechange = function () { alert(foo); }
}
When you call the first parameter foo
it's whatever's calling that callback passes in that's foo
inside the function. If you want to reference a previously declared variable just do that, make sure not to use a parameter with the same name.
回答2:
You can create a function like this
var c="hello";
(function(b){
alert(b)
})(c);
result would be "hello"
回答3:
You can also do this, but maybe it's not necessary:
function iClick(this)
{
var foo = "I would like to pass this.";
ajax.onreadystatechange = (function(thevar) {
return function () { alert(thevar); };
})(foo);
}
回答4:
As @John Hartsock referred, the answer that everyone should really remember is this
var c="hello";
(function(b){
alert(b)
})(c);
And that's very important for example in a for
loop when there is some async function inside it, because otherwise you don't get the correct item.
Tell me, what comes out from here?
for (var i=0; i<5; i++){
setTimeout(function(){
console.log(i);
}, 1000);
}
Exactly: all 5, because when all the timers are triggered after 1 second, variable i
is already at the value 5
.
But if you use a self-invoked anonymous function (SIAF) like this
for (var i=0; i<5; i++){
(function (j){
setTimeout(function(){
console.log(j);
}, 1000);
})(i);
}
it does work, since every time the function is evoked, it runs another instance of the function and as any function, it has its own local variables. I do not merely define the function, I also run it right away (through the ();
at the end), but then internally a new instance of the function will be created with different internal local variables, as I parse to the function a different variable every time I run it.
回答5:
I belive you wanted something like that
function handleAjaxRequest(params) {
var context = {'b':'inner', 'c': params['c']};
function rendered(html) {
// render
}
function gotPart(part) {
context['a'] = part;
engine.render(context).addCallback(rendered);
}
ajax.getPart(params).addCallback(gotPart);
}
来源:https://stackoverflow.com/questions/3946177/javascript-is-it-possible-to-pass-a-variable-into-a-callback-function-that-is-a