在JavaScript中使用“null”初始化变量是一个好习惯

Question

Which one makes more sense

var myVar = null;

myVar = someLogic(); //someLogic() might return a primitive or an object

if(myVar){
  //other logic
}

OR

var myVar;

myVar = someLogic(); //someLogic() might return a primitive or an object

if(myVar){
  //other logic
}

Answer 1

In JavaScript, there is generally no good reason to initialize variables to null .

In languages like C, variables should always be initialized before use because there is no guarantee as to the value of an uninitialized variable – it could be 0, 1, 2, or 283942, or anything. However, JavaScript has no such problem. In JavaScript, variables that have been declared but not initialized will always have the value undefined .

undefined is it's own type in JavaScript. When cast to a boolean, it becomes false .

undefined == null returns true , but undefined === null returns false .

Semantically, undefined means that a value has not been set, whereas null means that there is no value, but we might expect one. However, there is no hard rule for this, as you can always assign the value undefined to a variable manually – I wouldn't recommend this.

In general, setting uninitialized variables to null would be a waste of time.