Vertical bar, then zero

The title, expressed in words , was needed only for searchable finding. But it will be a question of the role of the character construct “ | 0 ” in JavaScript.

For the first time, I noticed it when I translated the FAQ about asm.js and read the specifications of this subset of the JavaScript language. There, " | 0 " serves, for example, to specify the type of value returned from a function: when we saw " | 0 " after a value, it means that we have a significant integer.

Suddenly, I noticed the construction “ | 0 ” in the example code on Github, where the conversion to a whole number of the result of dividing by 1024² took place.
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Then my eyes opened, and I saw wonderful opportunities:

( 3|0 ) === 3; //     ( 3.3|0 ) === 3; //       ( 3.8|0 ) === 3; //  ,      ( -3.3|0 ) === -3; //         ( -3.8|0 ) === -3; //   Math.floor(-3.3) == Math.floor(-3.8) == -4 ( "3"|0 ) === 3; //        ( "3.8"|0 ) === 3; //        ( "-3.8"|0 ) === -3; //         ( NaN|0 ) === 0; // NaN    ( Infinity|0 ) === 0; //       , ( -Infinity|0 ) === 0; //    , ( null|0 ) === 0; //   null, ( (void 0)|0 ) === 0; //   undefined, ( []|0 ) === 0; //    , ( [3]|0 ) === 3; //        , ( [-3.8]|0 ) === -3; //       , ( [" -3.8 "]|0 ) === -3; //         , ( [-3.8, 22]|0 ) === 0 //        ( {}|0 ) === 0; //       ( {'2':'3'}|0 ) === 0; //    ( (function(){})|0 ) === 0; //       ( (function(){ return 3;})|0 ) === 0; //    

So, first of all, we have a convenient means of discarding the fractional part.

• In relation to negative numbers, it is useful in that a fractional number is converted not to the nearest smaller integer (increasing in absolute value), as it would have happened after “ Math.floor () ”, but to the nearest smaller modulo integer (increasing in value ). Often this is exactly what is required.
  
• In relation to positive numbers, it is useful, especially because the construction of " | 0 " is more than an order of magnitude shorter compared to " Math.floor () ". Therefore, it can and should cause developers to get used no less than the “ $ () ” entry in jQuery, which I mentioned four days ago , that no one voluntarily goes back to “ document.getElementsByClassName () ”, for example .

Secondly, we have a convenient means of converting various types to whole numbers.

• It can pick out integers (and discard the fractional part of fractional numbers), extracting them from the strings (with the initial and final spaces discarded) and even from single-element arrays.
  
• In relation to the data of all other types (which can not be extracted), this tool acts as a universal zeroer. Often this is exactly what is required.

Observing the effect of this tool, you should compare it with the method (“ + ” before the value), which is recommended in “JavaScript Garden” (and after it in “JavaScript Garden” ) for conversion to number.

With such a comparison, it is immediately clear that plus converts to a fractional number, making possible such exotic variants of fractional numbers as minus infinity (obtained, for example, from “ + [“ -Infinity ”] ”) or NaN (from “ + {} ” ), whereas “ | 0 ” converts to an integer , and therefore exotic variants are reset.

I recommend this technique to be widely used in your javascript code as needed.