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JavaScript JavaScript Basics (Retired) Making Decisions with Conditional Statements Boolean Values

Posted by Katsumi Suno
Katsumi Suno
4,194 Points

Do we always have to assign an initial value to a variable when defining them?

Can we define a variable without an initial value and asign a value when needed? Or does this pose problems in JS?

var myVariable;

At a later point in the programm:

myVariable = true;

2 Answers

martinjones1
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martinjones1
Front End Web Development Techdegree Graduate 44,824 Points

Yes this is possible, it doesn't pose a problem in JS as long as you know yourself what the variables value or type should be and what actions you may want to take if the value cannot be updated.

In this case, the value of the variable will just be undefined.

The link below is useful for understanding this a bit further quickly:

https://github.com/getify/You-Dont-Know-JS/blob/master/up%20%26%20going/ch2.md#values--types

Katsumi Suno
Katsumi Suno
4,194 Points

Thank you for the resource! So if you wanna be sure to use the right type later on, you better asign a value, because the variable itself doesn't ever have a type like in C#, that's good to know.

martinjones1
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.a{fill-rule:evenodd;}techdegree seal-36
martinjones1
Front End Web Development Techdegree Graduate 44,824 Points
martinjones1
.a{fill-rule:evenodd;}techdegree seal-36
martinjones1
Front End Web Development Techdegree Graduate 44,824 Points

With var you could just keep setting it to any type and value that you want.

If you are familiar with a language like C#, then you could also look at TypeScript. I have started to use it recently and really like it, so you may have an advantage here making that jump as it may feel more at home to you.

Other than that, let and const instead of var, could offer a bit more specificity on how you want the variable to behave.

https://github.com/getify/You-Dont-Know-JS/blob/master/es6%20%26%20beyond/ch2.md#let-declarations

https://github.com/getify/You-Dont-Know-JS/blob/master/es6%20%26%20beyond/ch2.md#const-declarations

Hope this helps.