Summing method in javascript

Methods to implement summation in JavaScript: 1. Sum through the "function sumArr(arr){...}" method; 2. Sum through forEach traversal; 3. Through "eval(arr.join (" "))" method to sum.

The operating environment of this article: windows7 system, javascript version 1.8.5, Dell G3 computer.

Sum method in javascript

JS array sum method

Array summation, generally our idea is to traverse the array items , and then add up.

That’s it:

 function sumArr(arr){
      var sum = 0;
      for(var i = 0;i<=arr.length;i++){
    sum += arr[i];//前提是arr中各项是数字，而不是数字字符串
//如果是数字字符串：sum += Number(arr[i]);
    }
  return sum;
}

Or forEach traversal:

function sumArr(arr){
        var sum = 0;
        arr.forEach(function(val,index,arr){
              sum += val;
        })
    return sum;
}

There is also a more black-tech writing method:

function sumArr(arr){
        return eval(arr.join("+")) 
}//直接把他变成各个数的加法运算字符串

Of course there is this A widely praised way of writing functional programming:

function sumArr(arr){
        return arr.reduce(function(prev,cur){
            return prev + cur;
        },0);
}
//reduce方法有两个参数，一个是callbackfunction(回调函数)，
//二是设置prev的初始类型和初始值

There is a written test question: (This summarizes the article)

Given any non-negative integer, repeatedly accumulate the digits until the result is a single digit. For example, given a non-negative integer 912, the first accumulation is 9 1 2 = 12, the second accumulation is 1 2 = 3, 3 is a single digit, and 3 is returned when the loop terminates. Please program it.

function add(num){
    if(isNaN(num)) return;
    if(num<10) return num
    const res=num.toString().split(&#39;&#39;).reduce((sum,value)=>{
        return sum+Number(value)
    },0)
    return add(res);
}
add(345);
3

Recommended study: "javascript Advanced Tutorial"

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