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Can you override the truthy coercion of a JavaScript Object?
The Next CEO of Stack OverflowLength of a JavaScript objectWhat is the most efficient way to deep clone an object in JavaScript?How can I merge properties of two JavaScript objects dynamically?How do I remove a property from a JavaScript object?How do you get a timestamp in JavaScript?How do I check if an array includes an object in JavaScript?How do I test for an empty JavaScript object?How do I correctly clone a JavaScript object?How can I get query string values in JavaScript?Checking if a key exists in a JavaScript object?
The string coercion can be overwritten using the toString function.
The number coercion can be overwritten using the valueOf function.
The boolean coercion can be also overwritten using the valueOf function.
var foo =
toString: function()
console.log("To String");
return "bar";
,
valueOf: function()
console.log("Value Of");
return 5;
;
console.log(`$foo`);
console.log(+foo);
console.log(foo == true);
console.log(!!foo);I haven't been able to find a function that gets called for when an object needs to get converted to a truthy. Since x == true and !!x have different behaviors, then I am guessing that there is no function that changes that. I instead tried extending types whose truthy is false but the only value that gets accepted by Object.create is null which is almost identical to an object literal (has none of the Object.prototype properties).
javascript object coercion
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
add a comment |
The string coercion can be overwritten using the toString function.
The number coercion can be overwritten using the valueOf function.
The boolean coercion can be also overwritten using the valueOf function.
var foo =
toString: function()
console.log("To String");
return "bar";
,
valueOf: function()
console.log("Value Of");
return 5;
;
console.log(`$foo`);
console.log(+foo);
console.log(foo == true);
console.log(!!foo);I haven't been able to find a function that gets called for when an object needs to get converted to a truthy. Since x == true and !!x have different behaviors, then I am guessing that there is no function that changes that. I instead tried extending types whose truthy is false but the only value that gets accepted by Object.create is null which is almost identical to an object literal (has none of the Object.prototype properties).
javascript object coercion
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
The short answer is JavaScript does not have actual operator overloading, so there is no way to modify certain behaviors in the language specification since it's essentially a hardcoded behavior. One such example is the negation operator.
– Patrick Roberts
Mar 8 at 19:40
you might be able to alter the way a window property coerces, but not the actual object.
– dandavis
Mar 8 at 19:43
add a comment |
The string coercion can be overwritten using the toString function.
The number coercion can be overwritten using the valueOf function.
The boolean coercion can be also overwritten using the valueOf function.
var foo =
toString: function()
console.log("To String");
return "bar";
,
valueOf: function()
console.log("Value Of");
return 5;
;
console.log(`$foo`);
console.log(+foo);
console.log(foo == true);
console.log(!!foo);I haven't been able to find a function that gets called for when an object needs to get converted to a truthy. Since x == true and !!x have different behaviors, then I am guessing that there is no function that changes that. I instead tried extending types whose truthy is false but the only value that gets accepted by Object.create is null which is almost identical to an object literal (has none of the Object.prototype properties).
javascript object coercion
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
The string coercion can be overwritten using the toString function.
The number coercion can be overwritten using the valueOf function.
The boolean coercion can be also overwritten using the valueOf function.
var foo =
toString: function()
console.log("To String");
return "bar";
,
valueOf: function()
console.log("Value Of");
return 5;
;
console.log(`$foo`);
console.log(+foo);
console.log(foo == true);
console.log(!!foo);I haven't been able to find a function that gets called for when an object needs to get converted to a truthy. Since x == true and !!x have different behaviors, then I am guessing that there is no function that changes that. I instead tried extending types whose truthy is false but the only value that gets accepted by Object.create is null which is almost identical to an object literal (has none of the Object.prototype properties).
var foo =
toString: function()
console.log("To String");
return "bar";
,
valueOf: function()
console.log("Value Of");
return 5;
;
console.log(`$foo`);
console.log(+foo);
console.log(foo == true);
console.log(!!foo);var foo =
toString: function()
console.log("To String");
return "bar";
,
valueOf: function()
console.log("Value Of");
return 5;
;
console.log(`$foo`);
console.log(+foo);
console.log(foo == true);
console.log(!!foo);javascript object coercion
javascript object coercion
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
edited Mar 8 at 19:37
nick zoum
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
asked Mar 8 at 19:33
nick zoumnick zoum
2,58611539
2,58611539
The short answer is JavaScript does not have actual operator overloading, so there is no way to modify certain behaviors in the language specification since it's essentially a hardcoded behavior. One such example is the negation operator.
– Patrick Roberts
Mar 8 at 19:40
you might be able to alter the way a window property coerces, but not the actual object.
– dandavis
Mar 8 at 19:43
add a comment |
The short answer is JavaScript does not have actual operator overloading, so there is no way to modify certain behaviors in the language specification since it's essentially a hardcoded behavior. One such example is the negation operator.
– Patrick Roberts
Mar 8 at 19:40
you might be able to alter the way a window property coerces, but not the actual object.
– dandavis
Mar 8 at 19:43
The short answer is JavaScript does not have actual operator overloading, so there is no way to modify certain behaviors in the language specification since it's essentially a hardcoded behavior. One such example is the negation operator.
– Patrick Roberts
Mar 8 at 19:40
The short answer is JavaScript does not have actual operator overloading, so there is no way to modify certain behaviors in the language specification since it's essentially a hardcoded behavior. One such example is the negation operator.
– Patrick Roberts
Mar 8 at 19:40
you might be able to alter the way a window property coerces, but not the actual object.
– dandavis
Mar 8 at 19:43
you might be able to alter the way a window property coerces, but not the actual object.
– dandavis
Mar 8 at 19:43
add a comment |
1 Answer
1
active
oldest
votes
foo == true actually converts foo to a number, that's why valueOf works, but it's misleading.
You can try == true here to see which steps of the comparison algorithm are executed (disclaimer: I made that).
!foo however calls ToBoolean, which explicitly always returns true for an object. There is no way to override that behavior.
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
So if you dovar obj = valueOf: function() return true; ; console.log(obj == true),truewill be converted to1and then back totrue?
– nick zoum
Mar 8 at 21:17
Bothtrues will be converted to1.
– Felix Kling
Mar 8 at 21:18
so the expression is coerced to1 == 1?
– nick zoum
Mar 8 at 21:19
Yep. You can try it on the page I linked to.
– Felix Kling
Mar 8 at 21:20
Isn'tobjsupposed to be coerced to the same type as thetruethough?
– nick zoum
Mar 8 at 21:21
|
show 4 more comments
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foo == true actually converts foo to a number, that's why valueOf works, but it's misleading.
You can try == true here to see which steps of the comparison algorithm are executed (disclaimer: I made that).
!foo however calls ToBoolean, which explicitly always returns true for an object. There is no way to override that behavior.
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
So if you dovar obj = valueOf: function() return true; ; console.log(obj == true),truewill be converted to1and then back totrue?
– nick zoum
Mar 8 at 21:17
Bothtrues will be converted to1.
– Felix Kling
Mar 8 at 21:18
so the expression is coerced to1 == 1?
– nick zoum
Mar 8 at 21:19
Yep. You can try it on the page I linked to.
– Felix Kling
Mar 8 at 21:20
Isn'tobjsupposed to be coerced to the same type as thetruethough?
– nick zoum
Mar 8 at 21:21
|
show 4 more comments
foo == true actually converts foo to a number, that's why valueOf works, but it's misleading.
You can try == true here to see which steps of the comparison algorithm are executed (disclaimer: I made that).
!foo however calls ToBoolean, which explicitly always returns true for an object. There is no way to override that behavior.
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
So if you dovar obj = valueOf: function() return true; ; console.log(obj == true),truewill be converted to1and then back totrue?
– nick zoum
Mar 8 at 21:17
Bothtrues will be converted to1.
– Felix Kling
Mar 8 at 21:18
so the expression is coerced to1 == 1?
– nick zoum
Mar 8 at 21:19
Yep. You can try it on the page I linked to.
– Felix Kling
Mar 8 at 21:20
Isn'tobjsupposed to be coerced to the same type as thetruethough?
– nick zoum
Mar 8 at 21:21
|
show 4 more comments
foo == true actually converts foo to a number, that's why valueOf works, but it's misleading.
You can try == true here to see which steps of the comparison algorithm are executed (disclaimer: I made that).
!foo however calls ToBoolean, which explicitly always returns true for an object. There is no way to override that behavior.
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
foo == true actually converts foo to a number, that's why valueOf works, but it's misleading.
You can try == true here to see which steps of the comparison algorithm are executed (disclaimer: I made that).
!foo however calls ToBoolean, which explicitly always returns true for an object. There is no way to override that behavior.
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
answered Mar 8 at 19:38
Felix KlingFelix Kling
562k131871936
562k131871936
So if you dovar obj = valueOf: function() return true; ; console.log(obj == true),truewill be converted to1and then back totrue?
– nick zoum
Mar 8 at 21:17
Bothtrues will be converted to1.
– Felix Kling
Mar 8 at 21:18
so the expression is coerced to1 == 1?
– nick zoum
Mar 8 at 21:19
Yep. You can try it on the page I linked to.
– Felix Kling
Mar 8 at 21:20
Isn'tobjsupposed to be coerced to the same type as thetruethough?
– nick zoum
Mar 8 at 21:21
|
show 4 more comments
So if you dovar obj = valueOf: function() return true; ; console.log(obj == true),truewill be converted to1and then back totrue?
– nick zoum
Mar 8 at 21:17
Bothtrues will be converted to1.
– Felix Kling
Mar 8 at 21:18
so the expression is coerced to1 == 1?
– nick zoum
Mar 8 at 21:19
Yep. You can try it on the page I linked to.
– Felix Kling
Mar 8 at 21:20
Isn'tobjsupposed to be coerced to the same type as thetruethough?
– nick zoum
Mar 8 at 21:21
So if you do
var obj = valueOf: function() return true; ; console.log(obj == true), true will be converted to 1 and then back to true?– nick zoum
Mar 8 at 21:17
So if you do
var obj = valueOf: function() return true; ; console.log(obj == true), true will be converted to 1 and then back to true?– nick zoum
Mar 8 at 21:17
Both
trues will be converted to 1.– Felix Kling
Mar 8 at 21:18
Both
trues will be converted to 1.– Felix Kling
Mar 8 at 21:18
so the expression is coerced to
1 == 1?– nick zoum
Mar 8 at 21:19
so the expression is coerced to
1 == 1?– nick zoum
Mar 8 at 21:19
Yep. You can try it on the page I linked to.
– Felix Kling
Mar 8 at 21:20
Yep. You can try it on the page I linked to.
– Felix Kling
Mar 8 at 21:20
Isn't
obj supposed to be coerced to the same type as the true though?– nick zoum
Mar 8 at 21:21
Isn't
obj supposed to be coerced to the same type as the true though?– nick zoum
Mar 8 at 21:21
|
show 4 more comments
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The short answer is JavaScript does not have actual operator overloading, so there is no way to modify certain behaviors in the language specification since it's essentially a hardcoded behavior. One such example is the negation operator.
– Patrick Roberts
Mar 8 at 19:40
you might be able to alter the way a window property coerces, but not the actual object.
– dandavis
Mar 8 at 19:43