http://www.runoob.com/jsref/jsref-regexp-wordchar-non.html
http://www.runoob.com/js/js-obj-string.html
http://www.runoob.com/jsref/jsref-obj-string.html
http://www.runoob.com/js/js-objects.html
var a = []; undefined a [] var b = new Boolean(a); undefined b Boolean {true}__proto__: Boolean[[PrimitiveValue]]: true !!b true if(a){console.log(1)} VM64:1 1 undefined if(!!null){} undefined if(!!null){console.log(1)}else{console.log(2)} VM96:1 2 undefined if(!!undefined){console.log(1)}else{console.log(2)} VM115:1 2 undefined if(!!a){console.log(1)}else{console.log(2)} VM138:1 1 undefined a []
原文：https://www.cnblogs.com/whoknows1/p/10492221.html