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I just want to practice Javascript, so I try this easy code. In my expected that the output should be whole list.

When I use this code I only can get the output is 

[5, 9, 17, 14, 4, 19, 11, 8, 13, 10, 18, 15, 16, 20]

I did not know what happened on it, and where was 

[1,0,2,3,6,7,12...] 

var li = [5,9,17,14,1,0,4,19,11,6,8,13,10,2,18,15,16,3,12,7,20] var length = li.length; var x = []; for(var i = 0; i < length; i++){ if(!(li[i]in x)){ x.push(li[i]); }; } console.log(x);

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9
  • What do you want to achieve ? Commented May 3, 2018 at 7:45
  • [5,9,17,14,1,0,4,19,11,6,8,13,10,2,18,15,16,3,12,7,20] Commented May 3, 2018 at 7:45
  • 3
    all you need just simply console.log(li) Commented May 3, 2018 at 7:46
  • This is your input data. Commented May 3, 2018 at 7:46
  • 1
    x is an array, so when you say something in array it treats array as an object. 1 in x is true because x has property 1, which is index 1, that's why 1 don't get pushed in x Commented May 3, 2018 at 7:47

3 Answers 3

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8

the condition checking if(!(li[i]in x)){ is not correct. in check if keys(index) exist in the array .

Change to if(!x.includes(li[i])){

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See this thread for browser support info and alternative methods
3

From Javascript if in x I got

JavaScript does have an in operator, but it tests for keys and not values.

So you don't get those values because you check for the key -> 0, 1, 2, 3, etc. and at the position of e.g. item 1 in your list the 1st key is already used.

In other words what the if in your specific case actually does is if(x.length < li[i]).

Just to clarify if(x.length < li[i]) is not the same as !(li[i]in x) in every case!

To print the whole list use includes for your if. https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Global_Objects/Array/includes

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In other words what your if actually does is if(x.length < li[i]){. This is not true. x.length < li[i] is not the same as !(li[i]in x)
@Adelin, of course you are right the == is not right here! And you are also right with x.length < li[i] is not the same as !(li[i]in x), i never said that! But in @Steve's specific case x.length < li[i] has the same effect as !(li[i]in x) so he may got a better explanation for the in operator
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If you want to print each one at a line use console.log(li[I]); insidr the for loop, or remove everything and use console.log[li]; to print the whole array all together

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