Is var a data type in JavaScript?
JavaScript is a dynamic type language, means you don’t need to specify type of the variable because it is dynamically used by JavaScript engine. You need to use var here to specify the data type. It can hold any type of values such as numbers, strings etc.
How do you check if a VAR is defined in JavaScript?
To check if a variable is defined or initialized:
- Use the typeof operator, which returns a string indicating the type of the variable.
- If the type of the variable is not equal to the string ‘undefined’ , then the variable has been initialized.
- E.g., if (typeof a !== ‘undefined’) , then the variable is defined.
What will be the output of typeof []?
The typeof operator is used to get the data type (returns a string) of its operand. The operand can be either a literal or a data structure such as a variable, a function, or an object. There are six possible values that typeof returns: object, boolean, function, number, string, and undefined.
What is JavaScript VAR?
var is the keyword that tells JavaScript you’re declaring a variable. x is the name of that variable. = is the operator that tells JavaScript a value is coming up next. 100 is the value for the variable to store.
What is undefined data type in JavaScript?
undefined is a property of the global object. That is, it is a variable in global scope. A variable that has not been assigned a value is of type undefined . A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value.
How check variable is undefined or not in JavaScript?
Note: The undefined is not a reserved keyword in JavaScript, and thus it is possible to declare a variable with the name undefined. So the correct way to test undefined variable or property is using the typeof operator, like this: if(typeof myVar === ‘undefined’) .
How do you validate a variable in JavaScript?
Answer: Use the typeof operator If you want to check whether a variable has been initialized or defined (i.e. test whether a variable has been declared and assigned a value) you can use the typeof operator.
What is type of undefined in JavaScript?
undefined is a property of the global object. A variable that has not been assigned a value is of type undefined . A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not returned .
How do you write typeof in JavaScript?
JavaScript typeof operator
- Example: // “string” document.write( typeof ‘mukul’ + “<br>” ) // “number” document.write( typeof 25 + “<br>” ) // “undefined” document.write( typeof variable)
- Output: string number undefined.