Spread Operator in TypeScript

Spead Operator provides an elegant syntax for copying or combining elements from existing arrays or objects into new ones.

Array Manipulation

Copying an Array

One of the most common use cases of the spread operator is to create a shallow copy of an array. Let’s consider an example:

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const originalArray = [1, 2, 3];
const copiedArray = [...originalArray];

In this code snippet, the spread operator ... is used to spread the elements of the originalArray into a new array copiedArray. This ensures that modifying the copiedArray does not affect the originalArray, as they are separate instances.

Concatenating Arrays

The spread operator can also be used to concatenate arrays effortlessly. Suppose we have two arrays, array1 and array2, and we want to combine them into a new array combinedArray. We can achieve this using the spread operator:

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const array1 = [1, 2, 3];
const array2 = [4, 5, 6];
const combinedArray = [...array1, ...array2];

The resulting combinedArray will contain all the elements from array1 followed by all the elements from array2. This approach is much cleaner and more readable than using traditional methods like Array.concat().

Adding or Removing Elements

Using the spread operator, we can easily add or remove elements from an array. Consider the following example:

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const originalArray = [1, 2, 3];
const newArray = [...originalArray, 4, 5];

In this case, the spread operator is used to spread the elements of the originalArray and append additional elements 4 and 5 to create a new array newArray. Similarly, you can remove elements by excluding them using the spread operator.

Object Manipulation

Copying an Object

Just like with arrays, the spread operator can be used to create a shallow copy of an object. Let’s see an example:

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const originalObject = { name: 'John', age: 30 };
const copiedObject = { ...originalObject };

In this case, the spread operator is used to spread the properties of the originalObject into a new object copiedObject. This ensures that modifying the copiedObject does not affect the originalObject.

Merging Objects

The spread operator can also be used to merge multiple objects into a new object. Suppose we have two objects, object1 and object2, and we want to merge them into a new object mergedObject. We can achieve this using the spread operator:

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const object1 = { name: 'John' };
const object2 = { age: 30 };
const mergedObject = { ...object1, ...object2 };

The resulting mergedObject will contain all the properties from object1 and object2. If there are overlapping properties, the value from object2 will overwrite the value from object1.

Modifying Object Properties

The spread operator can also be used to modify specific properties of an object while keeping the rest intact. Consider the following example:

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const originalObject = { name: 'John', age: 30 };
const modifiedObject = { ...originalObject, age: 31 };

In the example above, the spread operator is used to spread the properties of the originalObject into a new object modifiedObject. The age property is also included and assigned a new value of 31. This creates a new object with the same properties as the originalObject, except for the modified property.

By using the spread operator in this way, you can easily modify specific properties of an object without mutating the original object itself. It provides a clean and concise syntax for object manipulation.

Rest Parameters

In addition to array and object manipulation, the spread operator can also be used with function parameters to handle variable-length arguments. This is often referred to as “rest parameters” in TypeScript.

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function sum(...numbers: number[]): number {
  return numbers.reduce((acc, curr) => acc + curr, 0);
}

const result = sum(1, 2, 3, 4, 5);
console.log(result); // Output: 15

In this example, the spread operator ... is used in the function parameter declaration ...numbers: number[]. It allows you to pass any number of arguments to the sum function, and TypeScript collects them into an array called numbers. The function then performs the sum operation on all the numbers in the array.

Rest parameters provide flexibility when dealing with functions that need to handle a variable number of arguments. The spread operator simplifies the process of passing and manipulating these arguments.

Cheers! 🍺