Defining: "this.isStartDateSet" vs. "!this.isStartDateSet"

Question

This is a variable declared in my code.

var startDateSet = $(this.parentEl).find('input[name=daterangepicker_start]').val();

I understand that '!' is essentially the same as 'not' but I do not understand what it means when used in this context

if (!this.isStartDateSet) {
    var
    var
    var
    ............

}

does this just mean "if this start date is not set?"

Thanny, thats not a default Javascript Method, if you could include the variable isStartDateSet, or is it the same as isStartDateCal — Mister SirCode, Nov 14 '19 at 01:32
The "logical NOT" operator will return `false` if the expression is _truthy_ which is very different than just checking if it's "not set" — Nick, Nov 14 '19 at 01:33
@Bobtroopo and Nick --> thank you. this is helping me understand. — thanny, Nov 14 '19 at 01:34
! operator is used to finding whether the mentioned variable is null or having some object. — Jayakumar Thangavel, Nov 14 '19 at 01:43

Word Rearranger · Accepted Answer · 2019-11-14T01:40:31.600

1

It would mean:

If isStartDateSet is falsy

Here is the list of falsy values:

edited Nov 14 '19 at 01:40

answered Nov 14 '19 at 01:31

Word Rearranger

score 0 · Answer 2 · answered Nov 14 '19 at 01:35

var startDateSet = $(this.parentEl).find('input[name=daterangepicker_start]').val();

This is checking if you have set a Starting or Beginning Date-Time on your input.

(like if you have put a start value into the input, or if it has no value at the moment)

Then, the function:

if (!this.isStartDateSet) {
    var
    var
    var
    ............

}

Is checking if there is NOT a starting date set, and is executing code inside of the conditional If statement.

2 Answers2