js Array vs []，以及是否为空的判断

var a = [],            // these are the same
b = new Array(),   // a and b are arrays with length 0

c = [‘foo‘, ‘bar‘],           // these are the same
d = new Array(‘foo‘, ‘bar‘),  // c and d are arrays with 2 strings

// these are different:
e = [3]             // e.length == 1, e[0] == 3
f = new Array(3),   // f.length == 3, f[0] == undefined

if (array === undefined || array.length == 0) {
    // array empty or does not exist
}