检查Javascript中是否存在值

Question

如何检查给定变量是否有值？什么是JS的等效PHP isset？

Answer 1

if (myVariable === undefined) {
    // myVariable has not been assigned a value...
}

此外，在Stackoverflow上询问并回答了同样的问题。 See, How can I determine if a JavaScript variable is defined in a page?

Answer 2

if(typeof variable === "undefined") {
    //code here
}