Using underscore.js for null checking

问题:

var name = "someName";
if(name !=null) {
   // do something
}

1. I am right now using http://underscorejs.org/#isNull, how would i do the same using underscore.js
2. Does it give any slight improvement in terms of performance for such functions.

回答1:

In underscore, you can use

if(!_.isNull(name)) {}

and in plain Javascript, you should use

if(name !== null) {}

You should avoid the loose inequality operator != because it does type coercion and undefined != null will return false.

Using plain Javascript is slightly faster because it doesn't have to invoke a function, but it will be imperceptible and it should hardly be a consideration.

I don't have a strong preference either way as far as readability goes, but it seems a little excessive and verbose to call a library function for such a simple check.

回答2:

Well your original code is flawed because if name is an empty string, false, the number 0 or any other falsy value then it will be considered null as far as your test is concerned.

As a general rule, calling ANY function is an overhead that should be avoided if possible. In this case, calling a function just to test if a value is null, when you could very easily just write if( name === null), is just stupid, IMO...

回答3:

In underscore.js you must write this to achieve that functionality.

var name = "someName";
if(!(_.isNull(name ))) {
   // do something
}

In underscore.js function isNull is written like this

_.isNull = function(obj) {
    return obj === null;
  };

So the difference is using == in your code and === in underscore.js.For more details about that difference you can look in this question.

Which equals operator (== vs ===) should be used in JavaScript comparisons?

P.S. I will suggest to write your own condition instead of using any library in such simple place.

var name = "someName";
if(name !== null)) {
   // do something
}

回答4:

if ((!(_.isUndefined(data)) || _.isEmpty(data))) {
//Valid Data 
}else {//Not Valid}