As far as i know it\'s not possible to modify an object from itself this way:
String.prototype.append = function(val){
this = this + val;
}
While strings are immutable, trying to assign anything to this
in any class will throw an error.
I've been researching the same... First of all, of course you can't just do this += x, 'this' is an object, you can't use the + operator on objects.
There are 'behind the scene' methods that get called - for example
String.prototype.example = function(){ alert( this ); }
is actually calling
String.prototype.example = function(){ alert( this.valueOf() ); }
So what you need to find is a relevant value that does the the opposite - something like this.setValue(). Except that there isn't one. The same holds for Number too.
Even the built in methods are bound by that
var str = 'aaa';
str.replace( /a/, 'b' );
console.log( str ); // still 'aaa' - replace acts as static function
str = str.replace( /a/, 'b' );
console.log( str ); // 'bbb' - assign result of method back to the object
On some other objects you can; for example on a Date:
Date.prototype.example = function(){
this.setMonth( this.getMonth()+6 );
};
var a=new Date();
alert(a.getMonth());
a.example();
alert(a.getMonth());
It's annoying, but there you go
The String primitives are immutable, they cannot be changed after they are created.
Which means that the characters within them may not be changed and any operations on strings actually create new strings.
Perhaps you want to implement sort of a string builder?
function StringBuilder () {
var values = [];
return {
append: function (value) {
values.push(value);
},
toString: function () {
return values.join('');
}
};
}
var sb1 = new StringBuilder();
sb1.append('foo');
sb1.append('bar');
console.log(sb1.toString()); // foobar
Strings are immutable; what you're asking is like saying, "Why can't I do:
Number.prototype.accumulate = function (x) {
this = this + x;
};
...?"