如何使用JavaScript检查两个值是否不等于null？

Question

I have the following code:

var store = window.localStorage;
var a = store.getItem('AccountID');
var b = store.getItem('CityID')

How can I make it so my refreshGrid("Page"); function only runs if both of these are set to values?

Answer 1

If you want to check that they are explicity null , just compare the values to null :

if(a !== null && b !== null) {
    //Neither is null
}

If you are storing values in there that should always evaluate to true , you can skip the equality checks (if nothing is stored in that particular storage item this will still fail, since null is falsy):

if(a && b) {
    //Neither is falsy
}

Answer 2

You can use this:

var a; var b;

if (a == null && b == null) {
   //a and b are null
}

OR

if (!a && !b) {
   //a and b are null, undefined, 0 or false
}

For James: alert(null == undefined) // returns true

Hope this helps.

Answer 3

Use a guard condition at the top of your function:

function myFunction() {
    if(a==null || b==null) return;
    // ... rest of the code here
}

Answer 4

I think the following code is what your looking for.

if(!!a && !!b){

  alert("this is not null")

}else{

  alert("this is null")

}