The easiest way to overwrite other functions with additional functionality
Example: Let's modify alert to keep a history array of all the messages we alert:
// initialize empty alertHistory array for the messages..
window.alertHistory = [];
// extend alert with additional functionality.
extendFunction('alert', function(args) {
// args is an array of the arguments alert was called with
// therefore, args[0] is the alert message.
// We'll push this onto the alertHistory array for reference later
alertHistory.push(args[0]);
});
// Test it!
alert('a message');
console.log(alertHistory);
if (alertHistory[0] === 'a message') {
console.warn('extendFunction worked!');
}So extendFunction takes 2 parameters: extendFunction(theFunction, extraFunctionality)
Now let's add " from DevinRhode2" to every alert message
extendFunction('alert', function(args, nativeAlert) {
// the second argument here is the nativeAlert function
// precisely, that's window.alert before it was modified
nativeAlert(args[0] + ' from DevinRhode2')
// because you called nativeAlert, extendFunction doesn't.
// however, if you don't call it, then extendFunction will
// If you don't want the original function called, then you should just overwrite the function:
// window.alert = function alertOverride() { ... };
});extendFunction also works for methods:
extendFunction('console.log', function(args, nativeConsoleLog) {
//omg console.log was called!
});But if your functions are not global like alert and console.log, then you need to do this:
localFunction = extendFunction(localFunction, function(args, originalLocalFunction) {
//your magic here!
});
//without extendFunction, it would look like this:
var oldLocalFunction = localFunction;
localFunction = function(paramA, paramB) {
// your magic here!
var args = Array.prototype.slice.call(arguments);
return oldLocalFunction.apply(this, args);
};Modify return values:
extendFunction('strangeModule.strangeMethod', function(args, prevFunc) {
var returnValue = prevFunc.apply(this, args);
returnValue.extraInfo = 'idk';
return returnValue;
});Or promises:
extendFunction('$.ajax', function(args, prevFunc) {
var stackOnSend = new Error().stack;
//prevFunc is the original $.ajax
//call that and store the value to return
var returnValue = prevFunc.apply(this, args);
returnValue.fail(function(){
console.error('request failed:', arguments, 'stackOnSend:', stackOnSend);
});
return returnValue;
});MIT licensed