node js check type of variable
Checking the Type of a Variable in Node.js
To check the type of a variable in Node.js, you can use the typeof
operator. The typeof
operator returns a string indicating the type of the operand. Here's how you can use it:
let variable = 42;
console.log(typeof variable); // Output: "number"
In the above example, the typeof
operator is used to check the type of the variable
, which is assigned the value 42
. The output will be "number"
, indicating that the type of the variable is a number.
It's important to note that the typeof
operator returns a string representation of the type, not the actual JavaScript type itself. The possible return values of the typeof
operator are:
"undefined"
: if the variable is declared but not assigned a value."boolean"
: if the variable is a boolean value (true
orfalse
)."number"
: if the variable is a number."bigint"
: if the variable is a BigInt."string"
: if the variable is a string."symbol"
: if the variable is a symbol."function"
: if the variable is a function."object"
: if the variable is an object ornull
.
It's worth noting that the typeof
operator has some quirks. For example, it returns "object"
for arrays and null
, and it returns "function"
for functions. To check if a variable is an array, you can use the Array.isArray()
method. To check if a variable is null
, you can use a simple equality check (variable === null
).
Here's an example that demonstrates these quirks:
let array = [1, 2, 3];
console.log(typeof array); // Output: "object"
console.log(Array.isArray(array)); // Output: true
let nullValue = null;
console.log(typeof nullValue); // Output: "object"
console.log(nullValue === null); // Output: true
let func = function() {};
console.log(typeof func); // Output: "function"
In the above example, the typeof
operator returns "object"
for the array
variable, even though it is an array. The Array.isArray()
method is then used to correctly determine if the variable is an array. Similarly, the typeof
operator returns "object"
for the nullValue
variable, but a simple equality check is used to determine if it is null
. Finally, the typeof
operator correctly returns "function"
for the func
variable, which is a function.
I hope this explanation helps! Let me know if you have any further questions.