方法:Boolean(变量)
注意:
★数字(非零)和字符串转完之后为true。
var n1=Infinity;
var n2="345";
var n3="前端";
console.log(Boolean(n1));//true
console.log(Boolean(n2));//true
console.log(Boolean(n3));//true
★undefined、null、0,空字符串转完之后为false.
var n4; console.log(Boolean(n4));//false var n5=null; console.log(Boolean(n5));//false var n6=0; console.log(Boolean(n6));//false var n7=""; console.log(Boolean(n7));//false