javascript - what does if(aa) mean

Question

if(aa) What exactly is it judging? (I was looking at other people’s code screenshots with these judgments. I didn’t understand the abbreviation)
Is it to judge whether aa is null or undefined??

Let’s assume Figure 2:

What is the if(aa) here judging??

Answer 1

First of all, the syntax of if expression is:

if (expression)
    statement

expressionexpression is executed. If the result is truthy (true value), statement is executed. If it is falsy (false value), it is not executed.

truthy and falsy in JavaScript. The false value is

false
undefined
null
0
-0
NaN
"" // the empty string

Except for these, the rest are true values.

Answer 2

Please search for keywords yourself: Implicit type conversion

Answer 3

If you don’t understand, you can ask questions

Answer 4

This is an if judgment expression. The specific syntax is as follows:

if (condition)
   statement1
[else
   statement2]

The value in condition needs to be of Boolean type true or false

In Javascript, the following values ​​will be implicitly converted to false:
0, -0, null, false, NaN, undefined, "" (empty string)
Other values ​​will be converted to true, please note that "false "It's also true.

Answer 5

if (aa) is equivalent to

if (!!aa){
    console.log('here goes true'); 
}