var varName = 'variant';

//瀏覽器環(huán)境

console.log(window.varName); //? => variant

console.log(self.varName);? //? => variant

// 通用環(huán)境下

console.log(this.varName);? //? => variant

//Node 環(huán)境下

console.log(global.varName);? // 報(bào)錯(cuò)

let letName = 'letName';

console.log(window.letName);? //undefined

console.log(this.letName)? ? //undefined