Mastering the Reduce Function: 10 Essential Techniques
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Chapter 1: Understanding the Reduce Function
As a front-end developer, you may have encountered the reduce function, a powerful and useful array method. Mastering its use can significantly boost both your coding efficiency and the quality of your code. The ten techniques discussed in this article are highly beneficial and can help minimize the amount of code you write!
The reduce method applies a provided callback function to each element of an array, accumulating a single result. It passes the return value of the previous element's calculation to the next, ultimately yielding a single value that reflects the operation performed across all elements.
The iterator function processes the elements sequentially, adding the current value to the result from the previous step until all elements are accounted for.
The parameters for reduce are as follows:
array.reduce(callback(accumulator, currentValue[, index[, array]])[, initialValue])
- callback (required): A function that processes each value in the array (initialValue except the first value if not provided).
- accumulator (required): The cumulative value returned from the last invocation of the callback; its initial value can be defined or will default to the first element of the array.
- currentValue (required): The element currently being processed in the array.
- index (optional): The index of the current element being processed.
- array (optional): The array upon which reduce() is called.
- initialValue (optional): The value passed as the first argument to the function on the first call. If not provided, the first element in the array will be used.
Note: If no initialValue is specified, the method starts executing from index 1, skipping the first element.
Section 1.1: Finding Maximum and Minimum Values
There are various methods to determine the maximum or minimum values within an array.
Using Math.max and Math.min is the most straightforward approach:
const arrayNumbers = [-1, 10, 6, 5, -3];
const max = Math.max(...arrayNumbers); // 10
const min = Math.min(...arrayNumbers); // -3
console.log(max=${max}); // max=10
console.log(min=${min}); // min=-3
Alternatively, you can achieve the same result using reduce:
const arrayNumbers = [-1, 10, 6, 5, -3];
const getMax = (array) => array.reduce((max, num) => (max > num ? max : num));
const getMin = (array) => array.reduce((min, num) => (min < num ? min : num));
const max = getMax(arrayNumbers); // 10
const min = getMin(arrayNumbers); // -3
console.log(max=${max}); // max=10
console.log(min=${min}); // min=-3
You can also define a function that accepts a type parameter:
const getMaxOrMin = (array, type = "min") =>
type === "max"
? array.reduce((max, num) => (max > num ? max : num)) : array.reduce((min, num) => (min < num ? min : num));
const max = getMaxOrMin(arrayNumbers, "max"); // 10
const min = getMaxOrMin(arrayNumbers, "min"); // -3
console.log(max=${max}); // max=10
console.log(min=${min}); // min=-3
Subsection 1.1.1: Summing an Array
Using reduce, you can effortlessly sum multiple numbers:
const sum = (...nums) => nums.reduce((total, num) => total + num);
console.log(sum(1, 2, 3, 4, 5)); // 15
You can also create an accumulator:
const accumulator = (...nums) => nums.reduce((acc, num) => acc * num);
console.log(accumulator(1, 2, 3)); // 6
Section 1.2: Parsing URL Search Parameters
Extracting search parameters from a URL is a common task. The conventional method involves splitting the string:
const parseQuery = (search = window.location.search) => {
const query = {};
search
.slice(1)
.split("&")
.forEach((it) => {
const [key, value] = it.split("=");
query[key] = decodeURIComponent(value);
});
return query;
};
console.log(parseQuery("?name=xiuerold&id=100")); // { name: 'xiuerold', id: '100' }
You can also use reduce to format the search parameters:
const parseQuery = (search = window.location.search) =>
search
.replace(/(^?)|(&$)/g, "")
.split("&")
.reduce((query, it) => {
const [key, value] = it.split("=");
query[key] = decodeURIComponent(value);
return query;
}, {});
console.log(parseQuery("?name=xiuerold&id=100")); // { name: 'xiuerold', id: '100' }
Chapter 2: Advanced Techniques Using Reduce
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Watch "7 Mastering Tips That Helped Me Get Better" for additional strategies to enhance your mastering skills.
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