javascript:将方法添加到字符串类

Question

我希望能在javascript中说出类似的内容:

   "a".distance("b")

如何将自己的距离函数添加到字符串类？

Answer 1

你可以扩展String原型;

String.prototype.distance = function (char) {
    var index = this.indexOf(char);

    if (index === -1) {
        alert(char + " does not appear in " + this);
    } else {
        alert(char + " is " + (this.length - index) + " characters from the end of the string!");
    }
};

......并像这样使用它;

"Hello".distance("H");

在这里查看JSFiddle.

Answer 2

String.prototype.distance = function( arg ) {
    // code
};

Answer 3

最小的例子：

没有人提到valueOf。

==================================================

String.prototype.
OPERATES_ON_COPY_OF_STRING = function ( 
    ARGUMENT 
){

    //:Get primitive copy of string:
    var str = this.valueOf();

    //:Append Characters To End:
    str = str + ARGUMENT;

    //:Return modified copy:
    return( str );
};

var a = "[Whatever]";
var b = a.OPERATES_ON_COPY_OF_STRING("[Hi]");
console.log( a ); //: [Whatever]
console.log( b ); //: [Whatever][Hi]

==================================================

从我对它的研究来看，没有办法就地编辑字符串。

即使您使用字符串对象而不是字符串原语。

下面不起作用并且在调试器中得到非常奇怪的结果。

==================================================

String.prototype.
EDIT_IN_PLACE_DOES_NOT_WORK = function ( 
    ARGUMENT 
){

    //:Get string object:
    var str = this;

    //:Append Characters To End:
    var LN = str.length;
    for( var i = 0; i < ARGUMENT.length; i++){
        str[LN+i] = ARGUMENT[ i ];
    };

};

var c = new String( "[Hello]" );
console.log( c );
c.EDIT_IN_PLACE_DOES_NOT_WORK("[World]");
console.log( c );

==================================================

Answer 4

经过多年（和 ES6）......我们有了一个新的选择来做到这一点：

Object.defineProperty( String.prototype, 'distance', {
	value: function ( param )
	{
		// your code …
		return 'counting distance between ' + this + ' and ' + param;
	}
} );

// ... and use it like this:
const result = "a".distance( "b" );
console.log(result);

Answer 5

你可以这样做:

String.prototype.distance = function (){ 
    //your code 
}