undefined。var foo = 1;var bar = "hello world";var i; // i === undefined
foo、bar、i三个变量。然后,foo 赋值为数值 1 ,bar 赋值为字符串 "hello world"。deletevoidtypeofnullundefinedNaNInfinityvarifelsetruefalserequirethisfunctionargumentsreturnforwhiledobreakcontinueswitchcasedefault
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