How to check if a value is not null and not empty string in JS

If you truly want to confirm that a variable is not null and not an empty string specifically, you would write:

if(data !== null && data !== '') {
   // do something
}

Notice that I changed your code to check for type equality (!==|===).

If, however you just want to make sure, that a code will run only for "reasonable" values, then you can, as others have stated already, write:

if (data) {
  // do something
}

Since, in javascript, both null values, and empty strings, equals to false (i.e. null == false).

The difference between those 2 parts of code is that, for the first one, every value that is not specifically null or an empty string, will enter the if. But, on the second one, every true-ish value will enter the if: false, 0, null, undefined and empty strings, would not.

Instead of using

if(data !== null && data !== ''  && data!==undefined) {

// do something
}

You can use below simple code

if(Boolean(value)){ 
// do something 
}

• Values that are intuitively “empty”, like 0, an empty string, null, undefined, and NaN, become false
• Other values become true

Both null and an empty string are falsy values in JS. Therefore,

if (data) { ... }

is completely sufficient.

A note on the side though: I would avoid having a variable in my code that could manifest in different types. If the data will eventually be a string, then I would initially define my variable with an empty string, so you can do this:

if (data !== '') { ... }

without the null (or any weird stuff like data = "0") getting in the way.