Index
Quand JavaScript se montre contre-intuitif.
1. Bugs
1.1. Sort
>> [3, 23, 1].sort()
Array(3) [ 1, 23, 3 ] (1) (2)| 1 | Should be [1, 3, 23]. Still buggy on Firefox Nightly ASAN 108.0a1 (2022-10-23) (64-bit) |
| 2 | From : https://solarpunk.moe/@alilly/109219021262612201 |
1.2. Attributes
2. Type conversions
2.1. Boolean
Everything is converted to true except :
false
null
undefined
NaN
0
"">> Boolean(-1)
true
>> Boolean('false')
true
>> Boolean(new Boolean(false)) (1)
true| 1 | typeof new Boolean(false) → 'object' |
>> true + true (1)
2
>> true + true + '' (2)
"2"
>> '' + true + true (3)
"truetrue"| 1 | true is converted to 1 in this context |
| 2 | The expression is successively Boolean, then converted to Number then converted to String |
| 3 | The Boolean values gets converted to String |
>> !'true' === !'false'
true2.2. Number
>> Number(undefined)
NaN
>> Number(null)
0
>> Number(false)
0
>> Number(true)
1
>> Number("")
0
>> Number("23.23e+2")
2323
>> Number("23.23s")
NaN>> typeof(NaN)
"number"2.3. String
>> String(undefined)
'undefined'
>> String(null)
'null'
>> String(false)
'false'
>> String(true)
'true'
>> String(23.23e+2)
'2323'
>> String(222e22)
'2.22e+24'2.4. Array
>> let arr = ['a', 'b', 'c']
>> arr.length--
>> arr
[ 'a', 'b' ]
>> arr.length++
[ 'a', 'b', <1 empty slot> ] (1)| 1 | Firefox Nightly ASAN 108.0a1 (2022-10-23) (64-bit). |
>> Array(16)
,,,,,,,,,,,,,,,, (1)
>> Array(16).join("wat")
watwatwatwatwatwatwatwatwatwatwatwatwatwatwatwat (2)
>> Array(16).joint("wat" + 1)
wat1wat1wat1wat1wat1wat1wat1wat1wat1wat1wat1wat1wat1wat1wat1wat1 (3)
>> Array(16).joint("wat" - 1) + " Batman!"
NaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaN Batman!| 1 | Empty array of 16 elements (what element ?) represented by comas |
| 2 | Join 16 strings "wat" |
| 3 | + for strings is a concatenation in JavaScript |
| 4 | - for strings gives NaN (Not a Number) |
3. Comparisons
3.1. Equality
Why should you use === in JavaScript ? Because == implies non evident implicit conversions.
>> 1 == '1'
true
>> null == undefined
true
>> null == false
false
>> NaN == NaN
false
>> "2" == true
false
>> "2" == false
false>> 1 === 1
true
>> 1 === '1'
false
>> null === undefined
false
>> NaN === NaN
false3.2. Math
>> Math.max() > Math.min()
false
>> Math.min()
Infinity
>> Math.max()
-Infinity4. for (… in …)
Iterates through object keys, not values. Use for (… of …) instead.
>> let obj = {
'0': "1st",
'1': "2nd",
'2': "3rd",
'length': 3
}
>> for (let p = 0; p < obj.length; p++) console.log(obj[p])
1st
2nd
3rd (1)
>>| 1 | Stops at p === 3 |
5. undefined
>> undefined = true
true
>> undefined
undefined (1)| 1 | undefined used to be overridable. Firefox Nightly ASAN 108.0a1 (2022-10-23) (64-bit). |
6. Operators
6.1. +
>> [] + []
(1)
>> [] + {}
[object Object]
>> {} + []
0
>> {} + {}
NaN| 1 | It gives and empty string |
7. Sources
8. Explore later
"Some broken functions in the library: parseInt, Date" - https://eamodeorubio.github.io/thejshorrorshow
Nim can compile to JavaScript.
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