What does ~fs.readdirSync mean in config files?

Question

In many javascript source code(mostly, config file), with code like

process.env.NODE_ENV = ~fs.readdirSync(configPath).map(function(file) {
    console.log(file);
    console.log(file.slice(0, -3));
    //The file is something like all.js. After use file.slice(0, -3) the output is like alljavascri
    return file.slice(0, -3);
}).indexOf(process.env.NODE_ENV) ? process.env.NODE_ENV : 'development';

My questions is, what does ~fs.readdirSync means? The ~ here doesn't look like xor.

do you have a specific example of a module where this is used? i'm not sure exactly why somebody would do this since ~[] === -1, but maybe seeing the inner map function would help. — aembke, Jul 03 '14 at 22:28
There's very likely more to the overall statement. Can you provide an example? — Jonathan Lonowski, Jul 03 '14 at 22:29
oh, ok your edit makes it more clear, the indexOf and ternary operation there completely change what this does. — aembke, Jul 03 '14 at 22:31

score 1 · Answer 1 · answered Jul 03 '14 at 22:22

1

~ is the bitwise NOT operator NOT. Every bit in x is inverted in ~x. For instance:

 x = 00011011
~x = 11100100

Alternatively, it is equivalent to doing XOR with 0xFFFFFFFF (all 1-bits):

     00011011
 XOR 11111111
     --------
   = 11100100

answered Jul 03 '14 at 22:22

Frxstrem

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I checked javascript logical operators but didn't find it https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators. And, what's the meaning of the entire line of code? thank you – wilbeibi Jul 03 '14 at 22:24
It's not a logical operator, it's a bitwise operator. The difference is that logical operators work on the whole operand and returns either true or false, while bitwise operators work on each bit of the operands and return an integer. – Frxstrem Jul 03 '14 at 22:27

What does ~fs.readdirSync mean in config files?

1 Answers1