如何在javascript上设置默认数据类型？

Question

I wanna set the javascript data type on my vars. ex:

var friends = {
  name: String(),
  age: Number(),
  classmate: Boolean()
};

Is this right? It works on the browsers. but I can't be certain. cause, below works too.

var friends = {
  name: '',
  age: 0,
  classmate: false
};

I want to know if these things are right or not or good or bad.

Answer 1

两者都是正确的，但是正确的方法是首先分配类型，在执行脚本和将值分配给变量的初始时间时将严格遵循。

Answer 2

Javascript is a weakly typed language, so this isn't doing anything for you. You do not need to declare the type of variables and you gain no protection by specifying a type when you initialize them. If you need strong typing, I would consider TypeScript ; otherwise, I would enjoy not having to deal with them.

Answer 3

First, javascript variables and properties are dynamic - they can take any values of any datatype. What you are actually doing in your example is some sort of casting.

var friends = {
  index1: Number("12"),
  index2: String("12")
};

If it's a good or bad thing to initialize your variables such way really depends on your requirements. If you want to ensure that the value of each variable is consistent all through out the scope (and prevent any exceptions or unwanted results), then I guess it would be a good practice for you.

Take for instance.

var sum = friends.index1 + friends.index2;
console.log(sum);

The result is "1212" and not 24. Hopefully this makes sense to you.

There are other ways to ensure that the value is of type that you expected. You can check it using typeof. Through this, you may no longer have to cast or "specify" the datatype during variable initialization.

if( typeof friends.index1 == "number" ) ...

Answer 4

In javascript values have a data type but variables don't. There is no mechanism to define the type of a variable and you can store any kind of value into an existing variable. (In some languages this kind of weak typed variable is called a variable of variant type).

For you information, ECMA script 2015 (ES6) introduced typed arrays that allow you to view a binary array buffer as an array of different length integer and floating point numbers. This is not specifically related to the wording of your question however, and is not the same as having typed variables.

Note the first example in the post does not give variables a data type. After

var friends = {
  name: String(),
  age: Number(),
  classmate: Boolean()
};

object property name contains a zero length string object, age contains 0 and classmate contains false, but you can reset them to anything afterwards.