JavaScript で配列を合計する 5 つの一般的な方法

var arr = [1,2,3];
function sum(arr) {
  var s = 0;
  for (var i = 0;i
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var arr = [1,2,3];
function sum(arr) {
  var s = 0;
  arr.forEach(function(val, idx, arr) {
    s += val;
  }, 0);
  return s;
};
console.log(sum(arr));//6

var arr = [1,2,3];
function sum(arr) {
  return arr.reduce(function(acr, cur){
    return acr + cur;
  });
}
console.log(sum(arr));//6

var arr = [1,2,3];
function sum(arr) {
  if(arr.length == 0){
    return 0;
  } else if (arr.length == 1){
    return arr[0];
  } else {
    return arr[0] + sum(arr.slice(1));
  }
}
console.log(sum(arr));//6

var arr = [1,2,3];
function sum(arr) {
  return eval(arr.join("+"));
};
console.log(sum(arr));//6