JavaScript - 使用字符串原型(prototype)函数做错事

Question

我正在尝试创建自定义字符串方法。

我不确定如何获取该方法所附加的字符串的值，传递给函数并返回。

function testPrototyping(passedVar) {
    passedVar += " reason why this is not working";
    return passedVar;
}

String.prototype.testMethod = testPrototyping;
var myVar = "some";
var myVar2;

// 1. This works but is not what I want:
myVar2 = myVar.testMethod(myVar);

// 2. This is what I want but doesn't work:
myVar2 = myVar.testMethod();

// 3. Wondering if this should work also:
myVar2 = testMethod(myVar);

Answer 1

您需要像这样使用this:

function testPrototyping() {
    var text = this;

    text = text.trim();

    text + " reason why this is not working";

    return text;
}

String.prototype.testMethod = testPrototyping;

“StackOverflow”.testMethod()

原型(prototype)方法中的关键字 this 引用构造函数实例。您可以阅读更多关于 "this"在这里。