数组reduce方法

reduce.js

//1.数组求和
var arr = [1,2,3,4];
var total = arr.reduce(function(pre, cur, index, arr){
    //接受四个参数：初始值（或者上一次回调函数的返回值），当前元素值，当前索引，调用 reduce 的数组
    //arr.reduce(callback,[initialValue])
    return pre + cur;
})
console.log(total)
//2.把二维数组转换为json键值对
var relArray = [
    ["Viola", "Orsino"],
    ["Orsino", "Olivia"],
    ["Olivia", "Cesario"]
];

var relMap = relArray.reduce(function(memo, curr) {
    memo[curr[0]] = curr[1];
    return memo;
}, {});

console.log(relMap);

/*Outputs: 
{
    "Viola": "Orsino",
    "Orsino": "Olivia",
    "Olivia": "Cesario"
}*/