'Const' declarations must be initialized in TypeScript

'Const' declarations must be initialized in TypeScript #

The error "const declarations must be initialized" occurs when we declare a variable using const but don't assign a value to it. To solve the error, specify a value in the same statement in which the variable is declared or use the let keyword instead.

Here is an example of how the error occurs.

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// ⛔️ 'const' declarations must be initialized.ts(1155)
const arr: string[];

We declared the arr variable using the const keyword, but didn't assign a value to it.

To solve the error, we have to assign a value to the const variable in the same statement in which it was declared.

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const arr: string[] = [];

What value you assign to the variable will depend on its type.

An alternative solution is to use the let keyword to declare your variable.

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let arr: string[];

arr = ['a', 'b'];

arr = ['c', 'd'];

console.log(arr); // 👉️ ['c', 'd']

When you use the let keyword, you can reassign the variable as many times as necessary.

If you declare a const variable without a value, you are effectively declaring an empty variable that cannot be reassigned and given a value later on, which must be a mistake.

We use a colon to give the variable a type and an equal sign to assign a value to it.

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const obj: { name: string } = { name: 'James Doe' };

Note that variables declared using const cannot be reassigned, but they are not immutable.

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const obj: { name: string } = { name: 'James' };
obj['name'] = 'Carl';

console.log(obj); // 👉️ {name: 'Carl'}

// ⛔️ Error: Assignment to constant variable.
obj = { name: 'Alan' };

The code snippet shows that we are able to change the value of an object declared using const, however trying to reassign the const variable causes an error - "Assignment to constant variable".

This is because you are not allowed to reassign or redeclare a variable declared using the const keyword.

Conclusion #

The error "const declarations must be initialized" occurs when we declare a variable using const but don't assign a value to it. To solve the error, specify a value in the same statement in which the variable is declared or use the let keyword instead.