javascript - How do I set a callback function parameter like 'data' in the "jQuery.ajax({ success : function(data)"? -

i wondering how set first parameter of callback function want, same way jquery in success callback or complete callback

i want this:

$.ajax({   success: function(data) {     alert(data)   } }); 

from understand close can want

function test(text) {   this.text = text   this.success = function(this.text) { } }  var = new test('king kong') a.success = function(k){   alert(k) } 

and want alert "king kong"

here's example of accepting callback in constructor function , calling later in response trigger. in below, trigger calling trigger function, can want:

function test(text, callback) {    this.text = text;   this.success = callback; }  test.prototype.trigger = function() {     // call success callback, passing in text     this.success(this.text); };  var = new test('king kong', function(k) {     alert(k); });  a.trigger(); 

(i've made test initially-capped there. that's convention constructor functions, of course free ignore.)

the key, fundamental thing understand functions objects else. can pass references them around, etc. call function, access whatever variable have function reference stored in , add parentheses (optionally function's arguments in parentheses).

consequently, of following call foo function , trigger alert:

function foo(msg) {     alert(msg); }  var f = foo;   // no parens, getting function reference, not calling f("hi there"); // we're calling var = {}; a.nifty = f; a.nifty("hi again");  function bar(func) {     func("hello third time"); } bar(foo);     // passing reference `foo` `bar` function, call 

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advanced: now, 1 thing jquery calls callback this value set specific (usually dom element related call). happen time call function via object property:

var = {name: "fred"}; a.func = function() {     alert(this.name); }; a.func(); // alerts "fred" 

...but that's not way can it; there's call , apply functions on function object itself:

var = {name: "fred"}; function func() {     alert(this.name); } func.call(a); // alerts "fred" 

there, function isn't assigned of a's properties, we've called function using call, accepts value this first argument. call passes on further arguments function you're calling:

function func(msg1, msg2) {    alert(this.name + " says " + msg1 + " , " + msg2); } var = {name: "fred"}; func.call(a, "one", "two"); // alerts "fred says 1 , two" 

apply same thing, accepts arguments pass on underlying function array instead of discrete arguments:

function func(msg1, msg2) {    alert(this.name + " says " + msg1 + " , " + msg2); } var = {name: "fred"}; func.apply(a, ["one", "two"]); // alerts "fred says 1 , two" //            ^------------^----- note these args array 

more reading: mythical methods