JS篇(012)- 复杂数据类型如何转变为字符串

// 1;
var obj = {
    valueOf: function() {
        return 1;
    }
};
console.log(obj + ""); //'1'
// 2;
var obj = {
    valueOf: function() {
        return [1, 2];
    }
};
console.log(obj + ""); //'[object Object]';
// 3;
var obj = {
    valueOf: function() {
        return [1, 2];
    },
    toString: function() {
        return 1;
    }
};
console.log(obj + ""); //'1';
// 4;
var obj = {
    valueOf: function() {
        return [1, 2];
    },
    toString: function() {
        return [1, 2, 3];
    }
};
console.log(obj + ""); // 报错 Uncaught TypeError: Cannot convert object to primitive value

var arr = [new Object(), new Date(), new RegExp(), new String(), new Number(), new Boolean(), new Function(), new Array(), Math] console.log(arr.length) // 9
for (var i = 0; i < arr.length; i++) {
    arr[i].valueOf = function() {
        return [1, 2, 3]
    }
    arr[i].toString = function() {
        return 'toString'
    }
    console.log(arr[i] + '')
}