Returns true if the specified value is undefined, false otherwise.
Use the strict equality operator to check if val is equal to undefined.
代码片段
const isUndefined = val => val === undefined;使用样例
isUndefined(undefined); // trueReturns true if the specified value is undefined, false otherwise.
Use the strict equality operator to check if val is equal to undefined.
const isUndefined = val => val === undefined;isUndefined(undefined); // true