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Message
TypeError: 'this' is not a Set object (EdgE) TypeError: Function.prototype.toString called on incompatible object (Firefox) TypeError: Function.prototype.bind called on incompatible target (Firefox) TypeError: Method Set.prototype.add called on incompatible receiver undefined (Chrome) TypeError: Bind must be called on a function (Chrome)
Error type
What went wrong?
When this error is thrown, a function (on a given object), is called with a this
not corresponding to the type expected by the function.
This issue can arise when using the Function.prototype.call()
or Function.prototype.apply()
methods, and providing a this
argument which does not have the expected type.
This issue can also happen when providing a function (stored in an object) as an argument to another function. In this case, the object won't the this
target of the function. To work-around this issue, you will either need to provide a lambda which is making the call, or use the Function.prototype.bind()
function to force the this
argument to the expected object.
Examples
Invalid cases
var mySet = new Set; ['bar', 'baz'].forEach(mySet.add); // mySet.add is a function, but "mySet" is not captured as this. var myFun = function () { console.log(this); }; ['bar', 'baz'].forEach(myFun.bind); // myFun.bind is a function, but "myFun" is not captured as this.
Valid cases
var mySet = new Set; ['bar', 'baz'].forEach(mySet.add.bind(mySet)); // This works due to binding "mySet" as this. var myFun = function () { console.log(this); }; ['bar', 'baz'].forEach(x => myFun.bind(x)); // This works using the "bind" function. It creates a lambda forwarding the argument.