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This article shares with you the content of sample analysis of if else and switch. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

The most basic if-else

Suppose there is a scenario where different values are printed under different circumstances.

Because there are too many conditions involved, we don't mention optimization such as trinocular operation.

If (a = = 1) {console.log ('a1')} else if (a = = 2) {console.log (' b2')} else if (a = = 3) {console.log ('c3')} else if (a = 4) {console.log (' d4')} / * n. , /

Now it can be seen, because the logic is simple, if the logic is complex, after iterating multiple versions, do you dare to move?

I tremble every time I move, and who knows where I will miss it.

What about another way?

Switch-case

This is a little clearer, and there seems to be no difference:

Switch (a) {case 1: console.log ('a1'); break; / * omitted. * / case 40: console.log ('a40'); break;}

Separate configuration information from execution action

Object mapping

Define an object as a configuration object to store different states, and look up through the linked list

Const statusMap = {1: () = > {console.log ('a1')}, 2: () = > {console.log (' b2')} / * n.... * /} / / execute let a = 1 statusMap [a | | 1] ()

This makes it clearer and separates the condition configuration from the specific implementation. If you want to add other states, just modify the configuration object.

Array mapping

Of course, in some states, you can use an array to do this configuration object.

/ / other optimizations are involved here, such as extracting the execution function, so just don't pay attention to the content of func. / / it is a function with complex content const statusArr = [function () {console.log (1)}, function () {console.log (2)},] / execute let a = 1statusArr [a | | 1] ()

Array is a little more demanding. If it is another key, such as a string, then the array cannot meet the demand.

Upgrade: same value for different key

This looks a little better, so the demand has changed again.

In the front, each treatment is different, and there are several cases where the processing function is the same.

For example, in the case of 1-39, b is called after calling aline 40, if we continue to deal with it in a mapped way.

Function F1 () {console.log (1)} function f2 () {console.log (2)} const statusMap= {1:f1, 2:f1, 3:f1, 4:f1, / / omit 40:f2} let a = 2statusMap [a] ()

This is fine, of course, but the code doesn't look concise enough to rewrite so many F1.

Before we start refactoring, let's get this straight. We just want to merge multiple key into one value.

In other words, our key value is not a string but an array. Object obviously only supports strings.

Then you can combine so many key into one:'1, 2, 3, 4, 4, 9'.

But there is something wrong with the search, and our parameters certainly can't match exactly.

Go on, whether to do a traversal plus a judgment, all included in the subset are considered to match, then the code looks like this.

/ / set the key value key to a concatenated string const statusMap = {'1Power2, 3jin4: F1: F1, / / omit 40: f2} / / get all the key values, then traverse with const keys = Object.keys (statusMap), len = keys.length// to get the corresponding value const getVal= (param='') = > {/ / the reason for using for loop is that there is no need to continue traversing for (let I = 0; I;

< len; i++) { const key = keys[i], val = statusMap[key] // 这里用什么来判断就随便了，两个字符串都有。 if (key.includes(param)) { return val } }}let a = 2, handle = getVal(a)handle() // 1 但是这样来看，增加了个遍历的过程，而且是拼接字符串，万一哪天传了个逗号进来，会得到了预料之外的结果。 map es6有个新的数据结构Map，支持任意数据结构作为键值。如果用Map可能更清晰一点。 /** * map键值索引的是引用地址， * 如果是下面这样的写法不好意思，永远得不到值 * map1.set([1,4,5],'引用地址') * map1.get([1,4,5]) //输出为undefined * 就像直接访问 * map1.get([1,2,3,4,5]) //同样为undefined */const map1 = new Map()const statusArr = [1,2,3,4,5]map1.set(statusArr,f1)// 预设默认值，因为不能直接遍历let handle = function(){}const getVal = (param = '') =>

{for (let value of map1.entries ()) {console.log (JSON.stringify (value)) if (value [0] .jump (param)) {console.log (value) / / can only handle handle = value [1]}} const a = 2getVal (a) handle ()

Personally, although this reduces repetitive code, it adds one more step to match the value, and the pros and cons vary.

Two-dimensional array

There must be some people who just don't want to do traversal. Since one array can't be satisfied, what about two arrays?

/ / keep the corresponding relationship between the key-value array and value const keyArr = ['1Power2, 3pje, 3pje, 5pje, p40'] const valArr = [f1Powerf2] const getVal = (param ='') = > {/ / find the subscript let index = keyArr.findIndex ((it) = > {return it.includes (param)}) / / get the corresponding value return valArr [index]} let a = 2, handle = getVal (a) handle ()

Use the subscript provided by the array to correspond key to value to get the desired value.

My original goal has not been achieved here, that is, the array repeated in the key can be matched without extra operations, and it has been dealt with anyway, which is not what lazy people want.

Thank you for reading! This is the end of this article on "sample Analysis of if else and switch". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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