Why applying Array.of() to Object creates Number in JavaScript/ECMAScript
I was reading ES spec and found that Array.of() uses this to create a new instance.
22.1.2.3 Array.of ( ...items )
Note 2: The
offunction is an intentionally generic factory method; it does not require that itsthisvalue be the Array constructor. Therefore it can be transferred to or inherited by other constructors that may be called with a single numeric argument.
Then I tried to create using Object as this, as following. However, it creates Number instance while the others like Date, RegExp or my classes create own instances.
const arr = Array.of.apply(Object, ['Hey']);
console.log(arr instanceof Number); // => true
console.log(Object.prototype.toString.apply(arr)); // => '[object Number]'
Why is this arr not instance of Object but Number?
Spec: https://www.ecma-international.org/ecma-262/9.0/index.html#sec-array.of
javascript
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
add a comment |
I was reading ES spec and found that Array.of() uses this to create a new instance.
22.1.2.3 Array.of ( ...items )
Note 2: The
offunction is an intentionally generic factory method; it does not require that itsthisvalue be the Array constructor. Therefore it can be transferred to or inherited by other constructors that may be called with a single numeric argument.
Then I tried to create using Object as this, as following. However, it creates Number instance while the others like Date, RegExp or my classes create own instances.
const arr = Array.of.apply(Object, ['Hey']);
console.log(arr instanceof Number); // => true
console.log(Object.prototype.toString.apply(arr)); // => '[object Number]'
Why is this arr not instance of Object but Number?
Spec: https://www.ecma-international.org/ecma-262/9.0/index.html#sec-array.of
javascript
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
add a comment |
I was reading ES spec and found that Array.of() uses this to create a new instance.
22.1.2.3 Array.of ( ...items )
Note 2: The
offunction is an intentionally generic factory method; it does not require that itsthisvalue be the Array constructor. Therefore it can be transferred to or inherited by other constructors that may be called with a single numeric argument.
Then I tried to create using Object as this, as following. However, it creates Number instance while the others like Date, RegExp or my classes create own instances.
const arr = Array.of.apply(Object, ['Hey']);
console.log(arr instanceof Number); // => true
console.log(Object.prototype.toString.apply(arr)); // => '[object Number]'
Why is this arr not instance of Object but Number?
Spec: https://www.ecma-international.org/ecma-262/9.0/index.html#sec-array.of
javascript
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
I was reading ES spec and found that Array.of() uses this to create a new instance.
22.1.2.3 Array.of ( ...items )
Note 2: The
offunction is an intentionally generic factory method; it does not require that itsthisvalue be the Array constructor. Therefore it can be transferred to or inherited by other constructors that may be called with a single numeric argument.
Then I tried to create using Object as this, as following. However, it creates Number instance while the others like Date, RegExp or my classes create own instances.
const arr = Array.of.apply(Object, ['Hey']);
console.log(arr instanceof Number); // => true
console.log(Object.prototype.toString.apply(arr)); // => '[object Number]'
Why is this arr not instance of Object but Number?
Spec: https://www.ecma-international.org/ecma-262/9.0/index.html#sec-array.of
javascript
javascript
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
edited Nov 19 '18 at 20:22
Ginpei
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
asked Nov 19 '18 at 19:43
GinpeiGinpei
17129
17129
add a comment |
add a comment |
1 Answer
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From the spec:
4. If IsConstructor(C) is true, then
a. Let A be ? Construct(C, « len »).
Given that C is Object and you are passing one argument to Array.of, this is the same as doing
new Object(1)
which returns a Number object (because that's how Object is defined).
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
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active
oldest
votes
From the spec:
4. If IsConstructor(C) is true, then
a. Let A be ? Construct(C, « len »).
Given that C is Object and you are passing one argument to Array.of, this is the same as doing
new Object(1)
which returns a Number object (because that's how Object is defined).
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
add a comment |
From the spec:
4. If IsConstructor(C) is true, then
a. Let A be ? Construct(C, « len »).
Given that C is Object and you are passing one argument to Array.of, this is the same as doing
new Object(1)
which returns a Number object (because that's how Object is defined).
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
add a comment |
From the spec:
4. If IsConstructor(C) is true, then
a. Let A be ? Construct(C, « len »).
Given that C is Object and you are passing one argument to Array.of, this is the same as doing
new Object(1)
which returns a Number object (because that's how Object is defined).
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
From the spec:
4. If IsConstructor(C) is true, then
a. Let A be ? Construct(C, « len »).
Given that C is Object and you are passing one argument to Array.of, this is the same as doing
new Object(1)
which returns a Number object (because that's how Object is defined).
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
answered Nov 19 '18 at 19:57
Felix KlingFelix Kling
550k126857913
550k126857913
add a comment |
add a comment |
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