I am trying to modify Javascripts Array type with a method which will push a value to an array only if its is not already present.
Here is my code:
// add a method conditionally
Array.prototype.method = function (name, func){
if(!this.prototype[name]){
this.prototype[name] = func;
return this;
}
};
// exclusive push
Array.method('xadd', function(value){
if(this.indexOf(value) === -1){
this.push(value)
};
return this;
});
However when I run the code the scratchpad in Firefox returns:
/*
Exception: TypeError: Array.method is not a function
@Scratchpad/3:19:1
*/
I want a vanilla way of doing this. Not a library as I am writing an open source library.
First I would run a check to see if the method is already on the array. Don't go overridding existing prototype methods. In addition, you're not adding func
to the prototype - you're adding it to the instances you'll be creating.
if (!('method' in Array.prototype)) {
Array.prototype.method = function (name, func) {
if (!this[name]) this[name] = func;
}
}
Then you need to actually create your array instance:
var arr = [1,2];
At which point you can use the method you created to add the function. Note in your question your check was incorrect:
arr.method('xadd', function (value) {
if (this.indexOf(value) === -1) {
this.push(value)
};
});
arr.xadd(3); // [1,2,3]
When you're putting a method on Array.prototype
the method will be available on the instances of Array.
// Add the custom method
Array.prototype.method = function() {
console.log('XXX');
}
var foo = [];
// prints XXX
foo.method();
Borrowing from Andy & Nihey I have arrived at the following solution which modifies the Array type making 'xadd' conditionally available to all instances of Array
if (!('xpush' in Array.prototype)) {
Array.prototype.xpush = function(value){
if(this.indexOf(value) === -1){
this.push(value);
};
return this
};
}
var a = [1,2,3];
console.log(a); // Array [ 1, 2, 3 ]
a.xadd(5);
console.log(a); // Array [ 1, 2, 3, 5 ]
a.xadd(3);
console.log(a); // Array [ 1, 2, 3, 5 ] '3' already present so not added
A better name would be xpush() as it's behaviour is a variant of push().
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