How to sum arrays in JavaScript

Methods for JavaScript array summation: 1. Use recursion to continuously add and sum the array elements; 2. Use for loops to continuously add and sum the array elements; 3. Use forEach to traverse and let the array The elements are continuously added and summed; 4. Use the "eval(arr.join(" "))" statement to sum.

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

JavaScript array summation

Method 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));
  }
}

Method 2. Regular loop:

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

Method 3. Functional programming map-reduce:

function sum(arr) {
  return arr.reduce(function(prev, curr, idx, arr){
    return prev + curr;
  });
}

Method 4. forEach traversal:

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

Method 5. eval:

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

//测试输出运行结果：
console.log(sum([ 1, 2, 3, 4 ]))

The following results can be obtained:

[Related recommendations: javascript learning tutorial]

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