JavaScript Function Overloading Undefined

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I have this code for a custom pop() method:

Array.prototype.pop = function(index) {
    if (typeof index === "undefined") {
        index = this.length - 1;
    var rtn = this.slice()[index];
    return rtn;

It works perfectly when I input a paramater (e.g. [1,3,5].pop(1) returns 3 and removes it). However, when I use it with no parameters (e.g. [1,3,5].pop()) it returns undefined and does not edit the array. I think it is to do with the fact that function overloading does not work with 0 parameters. Please can you help me find alternatives or a solution to this problem. Thanks.

If you want what I think you want (return the indexed value and remove it, or use the last value if no index), then this is what you want...

Array.prototype.pop = function(index) {
    if (typeof index === "undefined") {
        index = this.length - 1;
    // remove an array starting at index, with a length of 1,
    // and return the first value
    return this.splice(index, 1)[0];

// pop value by index
var arr = [1, 3, 5];


// pop last value
var arr = [1, 3, 5];


How to overload functions in javascript?, The issue is that JavaScript does NOT natively support method overloading. So, if it sees/parses two or more functions with a same name, it'll just  functions javascript This is a simple example of function overloading in JavaScript using closures to overload a Users.find() method, we can overload the method with either a name or a first name, last name.

You might also want to use a ForEach to loop and create a new array to fill the element only if the key is not the one provided in your arguments.

Also note that you can simplify your first check with some default value. Take a look (view online):

Array.prototype.pop = function(key = this.length - 1) {
    let array = [];

    this.forEach(function(element, index) {
      if( index !== key ) {

    return array;

console.log([1,3,5].pop(1)); // [1, 5]
console.log([1,3,5].pop()); // [1, 3]

Needless to say that overriding existing prototypes is strongly discouraged, you should probably think of another fancy name like Array.prototype.eject...

JavaScript Does NOT Support Method Overloading – That's True , Learn Function Overloading as part of the JavaScript Fundamentals Course for a value for each parameter and worry about accidentally printing undefined . Introduction. One of the strong points of JavaScript is that it is weakly typed, it allows a lot of flexibility, unfortunately this means that function overloading isn't available. We don't have explicit parameter type declarations, thus we cannot "type" parameters when we declare functions.

You don't even need check the type of index, the problem is that if no index is provided then index doesn't exist and you're trying to pass an actual value to a non-existent variable. What i would do is first change:

if (typeof index === "undefined")



For the sake of clarity.

Then within the if block change index = this.length - 1; for var index = this.length - 1;

var does the trick, as any variable is accessible outside that scope if declared with var.

Function Overloading, To begin, just as in JavaScript, TypeScript functions can be created both as a that it can't be given null or undefined , but rather, when the function is called, the Let's create a list of overloads that describe what our pickCard accepts and  The issue is that JavaScript does NOT natively support method overloading. So, if it sees/parses two or more functions with a same name, it’ll just consider the last defined function and overwrite the previous ones. In our case, the only function available is funcA(c).

Functions · TypeScript, Why: TypeScript chooses the first matching overload when resolving function calls. Because unspecified parameters appear as undefined in JavaScript,  When possible, I try to avoid method overloading since it creates a more complex API, both in terms of consumption, but also in terms of tested and implementation. That said, the type annotations of method and function overloading in TypeScript bring a much-welcomed clarity to the dynamic nature of JavaScript.

Do's and Don'ts · TypeScript, //experiement adding arity based function overloading to javascript. //to do. var overload = function (namespace,name,def){ if(namespace[loc] == undefined) {. Method overloading in TypeScript is a useful feature insofar as it allows you to create type definitions for existing libraries with an API that needs to be represented. When writing your own code, though, you may well be able to avoid the cognitive overhead of overloads using optional or default parameters.

function overloading in JavaScript · GitHub, A JavaScript function does not perform any checking on parameter values missing arguments (less than declared), the missing values are set to: undefined. A JavaScript function is defined with the function keyword, followed by a name, followed by parentheses (). Function names can contain letters, digits, underscores, and dollar signs (same rules as variables).

  • how about putting some kind of check ?
  • Array.remove does not exists indeed.
  • @AnwarNairi i created that method earlier in the js file, did not include it, sorry.
  • I was just about to suggest that exact edit, much cleaner
  • To make it even more succinct, you can use a default parameter and just write Array.prototype.pop = function(index = this.length - 1) { return this.splice(index, 1)[0]; }
  • @MBJH welcome. The only browser that doesn't have that implemented yet is IE (edge is fine), so if you have any concern of support for users with older windows os (or older browsers in general) you'd only want to use default parameter syntax if you're running your code through a preprocessor like babel.