Why won't this Javascript method keep calling itself?

Question

I have a JavaScript object with a privileged method. When this method has completed, I would like it to call itself (after a small timeout) and continue running indefinitely

Answer 1

Because this outside the function is not the same as this inside the function. Try instead:

function Test() {
    // ... private variables that testMethod needs to access ...
    var me = this;
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(me.testMethod, 2000);
    };
}

Answer 2

When you first call it with "myTest.testMethod();" the "this" keyword is bond to your "myTest" object, when the timeout fires the "window" object is bond to "this" keyword and "this.testMethod" is equivalent to "window.testMethod". Try:

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout((function(self){
            return function(){self.testMethod();};
        })(this), 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

Or:

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        var self = this;
        setTimeout(function(){self.testMethod();}, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

Answer 3

Try

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        var self = this;
        setTimeout(function() { self.testMethod(); }, 2000);
    };
}

or use setInterval.

Answer 4

because the this in your setTimeout is referring to the local function testMethod not Test -- essentially, you are saying setTimeout( testMethod.testMethod, 2000 )

function Test() {
    // ... private variables that testMethod needs to access ...
    var self = this;
    self.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(self.testMethod, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();