I am trying to understand equality in JavaScript. Here is the code.      var x = prompt("What is 10 + 10");     if (x === 10) {         document.write("Correct")     }     else {         document.write("Incorrect")     }   Why wouldn't I make the equals sign like "===". So if "10" is equal("===") to "x"(user answer) then it should be correct right?  I searched on both Stack Overflow and W3Schools, but couldn't find what I was looking for. I guess I'm just nor getting this "true or false" thing. I mean this seems like a very simple equation. Help would be great thanks guys!
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I'm using  to go through JavaScript, and it's returning many suggestions to replace == (two equals signs) with === (three equals signs) when doing things like comparing idSele_UNVEHtype.value.length == 0 inside of an if statement.  Is there a performance benefit to replacing == with ===?   Any performance improvement would be welcomed as many comparison operators exist.  If no type conversion takes place, would there be a performance gain over ==?
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I have a definition that claims that two sets are equal A = B, if and only if:  $\forall x ( x \in A \leftrightarrow x \in B)$  An empty set contains no elements. If I define the sets:  A = $\emptyset$  B = $\emptyset$  then can I conclude that A $\neq$ B? Since they contain no elements? Or would I have to show that an elements exists in one but not the other? To me it seems that these are not equal, but I'm struggling to wrap my head around this.  Thanks, Paul
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I'm trying to do my Maths assignment but I can't get this done. I can do other questions but this one is different. This is a picture of the question.   (source: )    My usual first step is to proof it when n = 1. But the problem is, that I don't know what x is. It says x is not equal to 1, but I still don't know what to do next.  Thank you.
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How do we show that equality holds in the triangle inequality $|a+b|=|a|+|b|$ iff both numbers are positive, both are negative or one is zero? I already showed that equality holds when one of the three conditions happens.
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What is the difference between == and ===?  How exactly does the loosely == comparison work? How exactly does the strict === comparison work?  What would be some useful examples?
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Both uses of the \let primitive often lead to the same result. Is this even true for every case? What was the thought process behind it. And if they are actually not equivalent, are there particular situations in which you can only use one or the other?  Addendum  Summary  As your plenty and nice answers show, there are cases in which you clearly have to respect one of the variations (for instance regarding assignments to '=' and macros that check for spaces). These were totally understandable points and they explain a lot. Now, @Werner's answer confirmed one ingenuous thought of mine:     "The use of = is purely to emphasize the fact that an assignment is being made [...]"   Moreover Knuth himself seem to have intended the synopsis including the '=', though he also used the other way. Why did he include it then? It will probabilly have to do with the exact meaning of the TeX source snippet cited by @Werner. To be honest, I don't know WEB either, but if there is someone who does, can he explain it (in very easy terms) by adding an edit to his answer? New answers are clearly welcome too.  Side Note  As an element of a gray area I found an example where using the syntax including the equal sign causes "difficulties":  If you have control sequences which need the 'csname-expandafter' mechanism, and you want to stick to the minimal exploitation of \expandafter by saying  \expandafter\let\csname foo1\expandafter\endcsname\csname bar1\endcsname   you can't add an equal sign because it would distract TeX from reading the \expandafters correctly. To get the equal sign work you would need to use the slightly unhandier version  \expandafter\let\csname foo1\expandafter\endcsname\expandafter=\csname bar1\endcsname
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I feel really stupid for asking this, but how do you form more complex if conditionals in TeX? I'm looking for something like:  \ifnum\x=1 OR \ifnum\x=14     {do this} \else     {do that} \fi   I don't want to have to resort to copy-pasting the entire condition just to change the expression when the body is the same.
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Is there any way I can specify a standard or custom numeric format string to always output the sign, be it +ve or -ve (although what it should do for zero, I'm not sure!)
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I just came over this syntax in some of the questions in this forum, but Google and any other searchengine tends to block out anything but letters and number in the search so it is impossible to search out "=>".  So can anyone tell me what it is and how it is used?
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I often use ($var &amp; 1) in my code, which returns true if $var is an odd number and false if it's an even number.  But what does "&amp;" actually do?
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I've seen an equals sign with a small exclamation mark on top being used to say "equals because of data that was given in the problem", for example for a boundary condition or initial value in a differential equation.  A rough picture of what I mean:       ! f(x) = 4   How do I typeset this in LaTeX? I've tried $=^!$ (which doesn't produce the desired result) and looked through the "relations" section of the  without success.
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I am doing , and am having a few problems with function notation. I understand the form f(x).  What does the form f: x ↦ y mean? Could you also give one or two examples?  And, if possible, state your source. Thank you.
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When should I use -eq vs = vs ==  e.g.    [[ $num -eq 0 ]]  [[ $num = 'zzz' ]]   I've observed a pattern of using -eq (and -ne, etc.) for numbers and = for strings.  Is there a reason for this and when should I use ==
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If I have a string of equations whose equal signs are aligned and one of the equations is too long and needs to span multiple lines, how do I create a second alignment. For instance, in the following example     \begin{align*}     f(x)&amp;=eqn1\\         &amp;=eqn2_part1+eqn2_part2\\          &amp;           +eqn2_part3\\         &amp;=eqn3\\          &amp;=eqn4\\   \end{align*}   How do I align the equals signs and the plus signs.
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A strict equality operator will tell you if two object types are equal. However, is there a way to tell if two objects are equal, much like the hash code value in Java?  Stack Overflow question  is similar to this question, but requires a more academic answer. The scenario above demonstrates why it would be necessary to have one, and I'm wondering if there is any equivalent solution.
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I am told that good developers can spot/utilize the difference between Null and False and 0 and all the other good "nothing" entities. What is the difference, specifically in PHP?  Does it have something to do with ===?
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What is the difference between == and === in php. I am unsure when to use both.  Updated note: So that it shows up in StackOverflow search, the difference between == and === is the same as the difference between != and !==.