JavaScript 数组操作：slice vs splice

　　在 JavaScript 中，对于数组的操作有两个很容易混淆的方法 splice, slice ，这里给大家推荐一篇介绍 splice, slice 二者区别的文章。

　　In JavaScript, mistaking

slice

for

splice

(or vice versa) is a common mistake among rookies and even experts. These two functions, although they have similar names, are doing two completely different things. In practice, such a confusion can be avoided by choosing an API that telegraphs the const-correctness of the function.

　　Array’s

slice

(ECMAScript 5.1 Specification Section 15.4.4.10) is quite similar to String’s

slice

. According to the specification,

slice

needs to accept two arguments, start and end. It will return a new array containing the elements from the given start index up the one right before the specified end index. It’s not very difficult to understand what slice does:

'abc'.slice(1,2)           // "b"
[14, 3, 77].slice(1, 2)    //  [3]

　　An important aspect of slice is that it does not change the array which invokes it. The following code fragment illustrates the behavior. As you can see, x keeps its elements and y gets the sliced version thereof.

var x = [14, 3, 77];
var y = x.slice(1, 2);
console.log(x);          // [14, 3, 77]
console.log(y);          // [3]

　　Although

splice

(Section 15.4.4.12) also takes two arguments (at minimum), the meaning is very different:

[14, 3, 77].slice(1, 2)     //  [3]
[14, 3, 77].splice(1, 2)    //  [3, 77]

　　On top of that,

splice

also mutates the array that calls it. This is not supposed to be a surprise, after all the name splice implies it.

var x = [14, 3, 77]
var y = x.splice(1, 2)
console.log(x)           // [14]
console.log(y)           // [3, 77]

　　When you build your own module, it is important to choose an API which minimizes this slice vs spliceconfusion. Ideally, the user of your module should not always read the documentation to figure out which one they really want. What kind of naming convention shall we follow?

　　A convention I’m familiar with (from my past time involvement with Qt) is by choosing the right form of the verb: present to indicate a possibly modifying action and past participle to return a new version without mutating the object. If possible, provide a pair of those methods. The following example illustrates the concept.

var p = new Point(100, 75);
p.translate(25, 25);
console.log(p);       // { x: 125, y: 100 }

var q = new Point(200, 100);
var s = q.translated(10, 50);
console.log(q);       // { x: 200, y: 100 }
console.log(s);       // { x: 210, y: 150 }

　　Note the difference between

translate()

that moves the point (in 2-D Cartesian coordinate system) and

translated()

which only creates a translated version. The point object p changed because it calls

translate

. Meanwhile, the object q stays the same since

translated()

does not modify it and it only returns a fresh copy as the new object s.

　　If this convention is used consistently throughout your application, that kind of confusion will be massively reduced. And one day, you can let your users sing I Can See Clearly Now happily!

　　link: /article/6368930.html


　　via ofilabs