Convert Undefined to 0 using JavaScript

Convert Undefined to 0 using JavaScript #

Use the ternary operator to convert an undefined value to zero, e.g. const result = val === undefined ? 0 : val. If the value is equal to undefined, the operator returns 0, otherwise the value is returned.

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let val = undefined;

val = val === undefined ? 0 : val;

console.log(val); // 👉️ 0

The ternary operator is very similar to an if/else statement.

The truthy values are all values that are not falsy.

The falsy values in JavaScript are undefined, undefined, false, 0, "" (empty string), NaN (not a number).

If the expression returns false, we return the value stored in the val variable.

An alternative approach is to use a simple if statement.

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let val = undefined;

if (val === undefined) {
  val = 0;
}

console.log(val); // 👉️ 0

Declaring the val variable with the let keyword allows us to reassign it if the stored value is equal to undefined.

While this approach is a little more verbose, it's still easy to read and intuitive.

Alternatively, you can use the logical OR (||) operator.

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let val = undefined;

val = val || 0;

console.log(val); // 👉️ 0

The logical OR (||) operator returns the value to the right if the value to the left is falsy.

An easy way to think about it is - the value to the right of the operator is a fallback in case the value to the left is falsy.