How to sum arrays in javascript

Summing method: 1. Use recursion to add the elements in the array one by one to sum; 2. Use for loop to add the elements in the array one by one to sum; 3. Use forEach to traverse , add the elements in the array one by one to calculate the sum; 4. Use eval() and join(), the syntax is "eval(arr.join(" "))".

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

Title description

Calculate the sum of all elements in the given array arr

Input description:

数组中的元素均为 Number 类型

Input example:

sum([ 1, 2, 3, 4 ])

Output example:

10

1. Regardless of algorithm complexity, use recursion:

function sum(arr) {
    var len = arr.length;
    if(len == 0){
        return 0;
    } else if (len == 1){
        return arr[0];
    } else {
        return arr[0] + sum(arr.slice(1));
    }
}

2. Regular loop

function sum(arr) {
    var s = 0;
    for (var i=arr.length-1; i>=0; i--) {
        s += arr[i];
    }
    return s;
}

3. forEach traversal:

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

4. eval:

function sum(arr) {
    return eval(arr.join("+"));
};

[Recommended learning: javascript advanced tutorial]

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