This question already has answers here:
Variable position in comparision in PHP
(4 answers)
Why do some experienced programmers write comparisons with the value before the variable? [duplicate]
(12 answers)
PHP conditional assignment
(1 answer)
Closed 2 years ago.
In many place, I've seen that there is used the expression if (value === expression) rather than if (expression === value).
For example, In php we use-
if (false === strpos('abc', 'a'))
And also I see after minifying JavaScript, the minified file also generated like this.
So my question is, what is the benefit of value === expression over expression === value?
Note: This question may be redundant but I may not get the proper keywords for searching. If it is duplicated then I am ready to close the question.
I don't think there is a difference because the idea of equality operator is that to check if both sides are have the same value, in === also same type.
Related
This question already has answers here:
Empty array does not equal itself in Javascript?
(4 answers)
Closed 1 year ago.
To check if an array is empty , we have many choices like if(array.length===0) or if(array=='') but I'm wondering why if (array==[]) doesn't check if an array is empty or not. Any one has a clear explanation?
Double Equals ( == ) checks for value equality only. It inherently does type coercion. This means that before checking the values, it converts the types of the variables to match each other. and in the same way [] doesn't have any type and if(arr == []) doesn't work in javascript
This question already has answers here:
JavaScript -- write a function that can solve a math expression (without eval)
(2 answers)
Closed 3 years ago.
I'm working on a problem generator that spits out phrases like "!(A && B) || (A || B)", but it does so in a string (I have a function that spits this out in string form). How would I convert this string expression into a same boolean expression in javascript? I've tried to use JSON.parse() but it keeps giving me an error.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval should be the function you're looking for, however read the note about the huge security risk!
This question already has answers here:
What does a tilde do when it precedes an expression?
(5 answers)
Closed 3 years ago.
code snippet of unirest
As you can see above, arrayIndexOf refers to a function. When invoking the arrayIndexOf function,
is it necessary to put "~" before "arrayIndexOf"? I try to change "~arrayIndexOf(value, field)" to "arrayIndexOf(value, field)". And it works as the same? Is there anything I miss?
In JavaScript, the tilde ~ Bitwise NOT operator is commonly used right
before an indexOf() to do a boolean check (truthy/falsy) on a string.
On its own, indexOf() returns the index number of a String object
passed in. So if -1 is returned it will be turned into 0 which is
falsy.
Source: https://wsvincent.com/javascript-tilde/
This question already has answers here:
What is the !! (not not) operator in JavaScript?
(42 answers)
Closed 7 years ago.
Maybe I am too quick in asking this question , but I was going through angular code and I found the logical expression evaluation like this :
https://github.com/angular/angular.js/blob/master/src/ng/directive/attrs.js#L362
Essentially an attribute was evaluated like :
attr.$set(attrName, !!value);
Is there a particular reason why was this done this way ?
!! is a concise way of ensuring that value will be a boolean.
This question already has answers here:
What does a tilde do when it precedes an expression?
(5 answers)
What exactly does ~ do? [duplicate]
(3 answers)
Closed 8 years ago.
I'm using and adapting the MVC example included in the Express.js repository.
In one of the modules, there's a JavaScript construct I'm not familiar with. The intent is to iterate through keys on an object and skip a few that are "reserved", but I don't understand what is happening with the tilde from a JavaScript perspective.
for (var key in obj) {
if (~['name', 'prefix', 'engine', 'before'].indexOf(key)) continue;
}
I'm reading it's a Bitwise NOT operator, but would appreciate an explanation in layman's terms of what that means, as well as what it's doing in this particular example.
indexOf returns -1 if not found. ~-1 is 0, i.e. false. So the whole things means: if key is found in the array, do continue.