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This is purely an educational question.
I'm working on a new version of a web app that the company I'm working for had made earlier. when re-writing the math, I came across this:
document.getElementById("estResidual").value-0;
Thinking there was no purpose for the "-0", I removed it. But when I tried the calculations, the numbers were waaayyyyyy off. Then I tried re-adding the "-0", and voila! everything worked nicely.
The Question: What did the "-0" do to change the value?
634
0 is an argument passed to void that does nothing, and returns nothing. JavaScript code (as seen above) can also be passed as arguments to the void method. This makes the link element run some code but it maintains the same page.
JavaScript actually has two different representations for zero: positive zero, represented by +0 (or just 0 ), and negative zero, represented by -0 . This is because JavaScript implements the IEEE Standard for Floating-Point Arithmetic (IEEE 754), which has signed zeroes.
Conceptually, zero (0) is a number, and NULL is a value that represents "no value". As such, 0 can be added, subtracted, etc., but NULL cannot. The NULL value for a variable can indicate, for example, that a variable has not yet been assigned a value.
for loops typically start with 0 instead of 1 . You can use the variable i in the code to be executed during the loop. The for loop increments the variable at the end of each loop. Once the condition is false, we exit the for loop.
It's an (ab)use of JavaScript's soft typing behavior. In this case, it will convert a string to a float:
> "13"
"13"
> "13"-0
13
> "1.01"-0
1.01
Unary + will do the same:
> +"13"
13
> +"9.9"
9.9
Note that using + will instead convert the integer 0 into a string and concatenate it:
> "13"+0
"130"
This is all standardized. For explicit details on how these operators should behave, you can always check the ECMAScript Language Specification (e.g. addition, subtraction. unary plus).
97
The JS engine re-casts on the fly to try and make statements work. So JS will cast "23" to an integer 23 when you try to perform math on it, and likewise it will convert integer 23 to string "23" if you do something like:
var a = 23;
console.log(23 + "asdf");
//outputs "23asdf"
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