setTimeout() is a great help to many JavaScript developers. For example, you may wish to add a delay to allow some animation to complete. This method is very easy to use.
The problem arises when you need to use it within a specific scope, for example when the function or method you are trying to call needs to be combined with the this keyword or when you need to send variables.
What we need to do is to get a reference to the initial scope as _this. _this is available to the code here because the functions that enclose it have access to the variables in the scope within which they have been enclosed. This is called “closure”. this is also available to the code here but will now refer to the scope local to this function, not the scope referenced by _this.
function createExample() {
// Define a simple application, creating scope
application = function () {
// Get a reference to the scope
_this = this;
// Create a method to start the timer
startTimer = function () {
setTimeout(function () {
// _this is available to the code here because the functions that
// enclose it have access to the variables in the scope within which
// they have been enclosed. This is called "closure".
// this is also available to the code here but will now refer to the
// scope local to this function, not the scope referenced by _this.
// Arguments can be supplied just as you always would
_this.show('Hello world');
} , 2000);
}
// Create a method to run when the timer has completed,
// complete with expected arguments
show = function (textToShow) {
console.log(textToShow);
}
// Once all methods have been defined, start the timer
this.startTimer();
}
// Once the application has been defined, start it
application();
}
// Usage
createExample();
