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This article mainly explains "how to use the reduce () method of JavaScript array". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn how to use the reduce () method of JavaScript array.

Subtract a value from each element in the array:

Var items = [5,10,15]; var reducer = function minus (minusSum, item) {return minusSum-item;} var total = items.reduce (reducer, 61); console.log (total); / / 31

In the above example, the initial value is of type number, so the returned result is also of type number. If we want to return a value of type object, we can also pass in the initial value of type object.

Var items = [5,10,15]; var reducer = function minus (minusSum, item) {minusSum.sum = minusSum.sum-item; return minusSum;} var total = items.reduce (reducer, {sum: 61}); console.log (total); / / {sum: 31}

Both of the above examples are simple uses of reduce (). Reduce () is a powerful method that we can also use to deal with more complex business logic.

For example, to find the total price of the goods in the shopping cart, the shopping cart data are as follows:

Var goodList = [{good: 'paper', price: 12}, {good:' book', price: 58}, {good: 'CD', price: 15}]

Then the total prices of all goods can be easily obtained by using the reduce () method:

Var count = goodList.reduce (function (prev, cur) {return cur.price + prev;}, 0); console.log (count); / / 85

If the user has a 10 yuan coupon, we just need to pass-10 as the initial value into the reduce () method.

Var count = goodList.reduce (function (prev, cur) {return cur.price + prev;},-10); console.log (count); / / 75

Let's add a little more difficulty to the example. The mall is engaged in sales promotion and there is a certain discount on the goods. how should we get the total price of the goods? It can also be easily solved by reduce method.

Var goodList = [{good: 'paper', price: 12}, {good:' book', price: 58}, {good: 'CD', price: 15}] Var dis = {paper: 0.5, book: 0.8, CD: 0.2} var count = goodList.reduce (function (prev, cur) {return cur.price + prev;},-10); var qcount = goodList.reduce (function (prev, cur) {return cur.price * dis [cur.good] + prev;}, 0); console.log (count, qcount); / / 75 55.4000000000006

Let's ignore the precision issue in JS here, because it focuses on the use of the reduce () method.

To give another example, how to find the number of occurrences of each letter in a string? It can be done if we don't use the reduce () method.

The code is as follows:

Var arrString = 'fghffgaga';var strArr = arrString.split (''); var rel = {}; var count = 1 for (var I = 0; I < strArr.length; I +) {for (strArr [I] = = strArr [j]) {count++; strArr.splice (j, 1); j = j-1 }} var qcount = count; count = 1; rel [strArr [I]] = qcount;} console.log (rel); / / {f: 3, g: 3, h: 1, a: 2}

The code that uses the reduce () method is as follows:

Var arrString = 'fghffgaga';var rel = arrString.split (''). Reduce (function (res, cur) {res [cur]? Res [cur] + +: res [cur] = 1 return res;}, {}) console.log (rel); / / {f: 3, g: 3, h: 1, a: 2}

Haha, isn't the code much simpler if you use the reduce () method to deal with it?

We can use the reduce () method to do various treatments on each element in the array, converting one type of array to another.

Var arr = [1,2] .reduce (function (res, cur) {res.push (cur +'); return res;}, []); console.log (arr); / / ["1", "2"] so far, I believe you have a better understanding of how to use the reduce () method of the JavaScript array, so you might as well do it! Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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