JavaScript深入理解

[leibnizli]

var x = 20;
(function() {
    if (x === 20) {
        var x = 30;
    }
    return x;
}()); // -> undefined

[leibnizli]

var a = [].concat([[1],[2]]);
var b = [].concat.apply([],[[1],[2]]);
console.log(a) //[[1],[2]]
console.log(b) //[1,2]