What is an uncaught TypeError in JavaScript?
According to the Mozilla website for developer documents, “the TypeError object represents an error when a value is not of the expected type.” Uncaught means that the error was not caught in the catch part of the try-catch block.
Code
Let’s go over some examples of the causes of the uncaught type error.
Uncaught TypeError: cannot read property ‘bar’ of null
let val = null;console.log(val.bar);
Note:
nullhas no properties to read or set.
Uncaught TypeError: cannot set property ‘bar’ of undefined
let val = null;val.bar = 20;
Note:
undefinedhas no properties to read or set.
Uncaught TypeError: undefined is not a function
let val = null;console.log(val());let num = 20;console.log(num());
Note:
undefinedis not a function. Similarly, an object, string, array, etc. is not a function either.
Uncaught TypeError: cannot use ‘in’ operator to search for ‘x’ in ‘y’
let val = "Hello from Educative!";console.log("Hello" in val);
Note: The
inoperator can only be used to check whether or not a property is in an object.
Uncaught TypeError: converting circular structure to JSON
let a = { b: "" };let b = { a: a };a.b = b;JSON.stringify(a);
Note:
acontains a reference tob, and vice versa, which makes variableaa circular data structure.JSON.stringify()only works with cyclic data structures.
For more details, refer to the official documentation on TypeError.
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