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Methods to Search Arrays in JavaScript

Methods to Search Arrays in JavaScript
Hostman Team
Technical writer
JavaScript
27.11.2023
Reading time: 6 min

Searching in an array is not a difficult task for a programmer. One immediately thinks of searching through a for loop or binary search in a sorted array with "greater than" and "less than" operations defined for its elements. But like any high-level programming language, JavaScript offers the developer built-in functions to solve various problems. In this article, we'll look at four JavaScript array search methods: find, includes, indexOf, and filter.

indexOf

indexOf is a function to search for an element in an array. This method searches for the object and returns its index or -1 if it does not find a matching one.

Syntax

Array.indexOf (search element, starting index)

Where:

  • Array is our array

  • search element is the element we are searching for;

  • starting index is the index from which we start the search. This argument is optional. By default, the function starts at index 0, i.e., the method checks the whole Array. If the starting index is greater than or equal to Array.length, the method immediately returns -1 and terminates. 

If the starting index is negative, JS treats it as an offset from the end of the array: if the starting index = -1, only the last element will be checked; if -2, then the last two, etc. 

Practice

Let's try the method in practice. Let's run this code and check the results:

let ExampleArray = [1,2,3,1,'5', null, false, NaN,3];

console.log("Position of 1", ExampleArray.indexOf(1) );
console.log("Position of the next 1", ExampleArray.indexOf(1,2) );
console.log("Position of 3", ExampleArray.indexOf(3) );
console.log("Position of 3 if starting index is negative", ExampleArray.indexOf(3,-2) );
console.log("Position of false", ExampleArray.indexOf(false) );
console.log("Position of 5", ExampleArray.indexOf("5") ); 
console.log("Position of NaN", ExampleArray.indexOf(NaN));

As a result of this code's operation, we obtained the following output: 

Position of 1 0
Position of the next 1 3
Position of 3 2
Position of 3 if starting index is negative 8
Position of false 6
Position of 5 -1
Position of NaN -1

indexOf searches for an element in the array from left to right and stops at the first matching element. This is clearly shown in the example with 1. To go from right to left, use the LastIndexOf method with a similar syntax.

Strict comparison (===) is used to compare the object we're searching for and the next object. When using strict comparison for different data types but with the same value, for example 5, '5' and "5" JavaScript gives a negative result, so IndexOf did not find 5

It's also worth remembering that indexOf does not handle NaN correctly. So, you need to use other methods to work with this value.

includes

includes does not exactly search for a given element in the array, but checks if it is there at all. It works in the same way as indexOf. includes returns True if it found the searched item and False if it didn't. Unlike indexOf, includes handles NaN correctly.

Syntax

Array.includes (search element, starting index)

Where: 

  • Array is our array

  • search element is the element we are searching for

  • starting index is the index from which we start searching. It's an optional argument; by default, the function starts at index 0, i.e., the method checks the whole Array. If the starting index is greater than or equal to Array.length, the method immediately returns False and terminates.  

If the starting index is negative, JS treats it as an offset from the end of the array: if the starting index = -1 only the last element will be checked; if -2 , then the last two elements will be checked, etc.

Practice

Let's slightly modify the code from the previous example and run it:

let Example = [1,2,3,1,'5', null, false,NaN, 3];

console.log("Presence of 1", Example.includes(1) );
console.log("Availability of the next 1", Example.includes(1,2) );
console.log("Presence of 3", Example.includes(3) );
console.log("Presence of 3 if starting index is negative", Example.includes(3,-1) );
console.log("Presence of false", Example.includes(false) );
console.log("Presence of 5", Example.includes(5) ); 
console.log("Presence of NaN", Example.includes(NaN) ));

Output:

Presence of 1 true
Presence of the next 1 true
Presence of 3 true
Presence of 3 if the starting index is negative true
Presence of false true
Presence of 5 false
Presence of NaN true

There is no alternative function that searches the JS array from right to left, which is not really necessary.

find

Suppose we need to find an object in an array. But we want to find it not by its value, but by its property. For example, we want to find a number in an array with a value between 15 and 20. As before, we can use a for loop, but it's not very convenient. To search with a specific condition, JavaScript has a find method.

Syntax

Array.find(function(...){
//if the item matches the condition (true), the function returns it and terminates;
//if nothing is found, it returns undefined
})

 Here:

  • Array is our array

  • function(...) is a function that sets the conditions.

Practice

As in the past examples, let's try out the method:

let ExampleArray = ["Hostman", 55555, "Cloud", "server provider", "guide"];
console.log(ExampleArray.find(element => element.length == 5))

Output:

Cloud

In this example, we searched for strings with a length of 5 characters. For numeric data types, the length is undefined, so 55555 is not appropriate. Find finds the first element and returns it, so guide was also not included in the result of our function. To find several elements that match a condition, we need to use the filter method.

Also, we should not forget about the findIndex method. It returns the index of the matching element. Or -1 if there is none. Otherwise, it works the same way as find.

filter

find searches for and returns the first element that matches the search conditions. In order to find all such elements, you need to use the filter method. The result of this function is an array (if nothing is found, it will be empty).

Syntax

Array.find(function(...){
//if the element matches the conditions (true), then add it to the final result and continue the search;
})

 Here:

  • Array is our array

  • function(...) is the function that sets the conditions.

Practice

Let's imagine the following task: we have a list of cuboids (rectangular parallelepipeds) with the lengths of their edges, and we need to output all cuboids with a certain volume. Let's write the code that realizes the solution of this task:

let ExampleArray = [
  [10, 15, 8],
  [11, 12, 6],
  [5, 20, 1],
  [10, 10, 2],
  [16,2, 4]
  ];

console.log(ExampleArray.filter(element=> element[0]*element[1]*element[2]>300)))

Output:

[ [ 10, 15, 8 ],
[ 11, 12, 6 ] ]

In this example, we found rectangular parallelepipeds with a volume greater than 300. In general, the filter method in JS allows you to implement all kinds of search conditions. 

Conclusion

In this article, we have learned about search methods in JavaScript and how to use them. All the above methods are universal tools for developers. But, like any universal tools, they are not always the most productive. For example, binary search will be much more efficient than find and filter.

JavaScript
27.11.2023
Reading time: 6 min

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Key methods include getDate(): Returns the day of the month. getFullYear(): Returns the four-digit year. getMonth(): Returns the month (0-11, where 0 represents January). getHours(): Returns the hour (0-23). getMinutes(): Returns the minutes (0-59). getSeconds(): Returns the seconds (0-59). For example, to retrieve the current date and format it as MM/DD/YYYY HH:MM:ss: function formatDate(dateObject) { const year = dateObject.getFullYear(); const month = dateObject.getMonth() + 1; // Months are zero-indexed const day = dateObject.getDate(); const hours = dateObject.getHours(); const minutes = dateObject.getMinutes(); const seconds = dateObject.getSeconds(); return `${month}/${day}/${year} ${hours}:${minutes}:${seconds}`; } console.log(formatDate(new Date())); Here is the result when executing the function.  There are however interesting methods we can use to format datetime into readable formats.  Formatting Date and Time JavaScript provides methods to format datetime values into human-readable strings. This allows developers to convert a Date object to a string or vice versa. Formatting a Date as a String To output a Date object as a human-readable string, use methods like toDateString() and toTimeString(): const currentDate = new Date(); const dateString = currentDate.toDateString(); console.log(dateString); const timeString = currentDate.toTimeString(); console.log(timeString); Here is the output: Converting Strings to Date Objects Developers can also convert readable strings into Date objects using the Date constructor: const dateFromString = new Date("October 10, 2024");console.log(dateFromString); However, it’s better to use recommended formats.  Recommended Formats To avoid errors when working with date strings, it is advisable to use reliable formats: ISO 8601 Format (Recommended): The safest and most reliable format is the ISO 8601 date format: YYYY-MM-DDTHH:mm:ss.sssZ. If only the date part is provided, it assumes the time as midnight 00:00:00. const date = new Date("2024-10-10T14:48:00Z");console.log(date); RFC2822 Format: Another accepted format is the RFC2822 format commonly used in email headers: Day, DD Mon YYYY HH:mm:ss GMT. const date = new Date("Wed, 10 Oct 2024 14:48:00 GMT");console.log(date); We now know how to format datetime values using the Date object. Let’s see how to manipulate date values for simple scheduling and calculations. Manipulating Date Values Date manipulation is essential for tasks like scheduling and calculating deadlines. JavaScript provides setter methods for modifying specific components of a Date object. Modifying Date Components Developers can modify specific components of a Date object using setter methods. Note that months are zero-indexed: let date = new Date(); date.setFullYear(2025); date.setMonth(5); // Set month to June date.setDate(15); // Set day to 15th date.setHours(10); // Set hour to 10 AM date.setMinutes(30); // Set minutes to 30 date.setSeconds(45); // Set seconds to 45 console.log(date); Adding or Subtracting Days Developers can easily add or subtract days using setDate(): let date = new Date(); date.setDate(date.getDate() + 5); // Add 5 days console.log(date); Date arithmetic can be accomplished using timestamps (milliseconds since January 1, 1970): let now = new Date(); let oneDayInMs = 24 * 60 * 60 * 1000; let tomorrow = new Date(now.getTime() + oneDayInMs); console.log(tomorrow); Comparing Date Objects Date objects can be compared using their timestamps: let date1 = new Date('2024-10-10'); let date2 = new Date('2024-12-25'); console.log(date1 > date2); // false (October 10 is earlier than December 25) console.log(date1 < date2); // true console.log(date1.getTime() === date2.getTime()); // false Now that we now how to manipulate dates values for calculation, let’s see how we can handle dates with time zones. Working with Time Zones The Date object is timezone-agnostic, meaning it doesn't have a built-in concept of time zones. However, JavaScript’s Date object handles dates in local time (system time zone) and UTC. When creating Date objects, it is essential to be aware of time zone conversions, especially when performing operations across different regions. Local Time vs. UTC JavaScript can work with localtime and UTC. Local time allows you to represent the time by the Date object when created without any specific time zone information, reflecting the local time of the environment in which JavaScript is executed. For example, creating a Date object in Paris will reflect the central European time zone. UTC is the time standard not affected by time zones or DayLight Saving Time (DST). Using Coordinated Universal Time (UTC) ensures consistency and avoids ambiguity when working with dates and times across different time zones, simplifying time calculations, logging, and user experience management in applications that serve users in multiple regions. Creating Date Objects in UTC To create a Date object in UTC, use the ISO 8601 format: const utcDate = new Date("2024-10-10T14:30:00Z");console.log(utcDate); Converting Local Time to UTC To retrieve UTC date components, use getUTCDate(), getUTCMonth(), etc.: const localDate = new Date();console.log(localDate.getUTCDate(), localDate.getUTCMonth() + 1, localDate.getUTCFullYear()); Converting UTC to Local Time Similarly, to convert a UTC date to local time, you can use the local equivalent methods: const utcDate = new Date("2024-10-10T14:30:00Z"); // UTC date const localDay = utcDate.getDate(); const localMonth = utcDate.getMonth() + 1; // Months are zero-indexed const localYear = utcDate.getFullYear(); console.log(`Local Date: ${localMonth}/${localDay}/${localYear}`); Being mindful of time zones when working with dates in JavaScript is essential for ensuring accurate datetime representation, especially in applications that require coordination across different regions. Let’s learn more about common Date Object methods. Common Date Object Methods JavaScript provides several static and instance methods that simplify working with dates. Here are some key methods: Date.now(): Returns the current timestamp in milliseconds since January 1, 1970. Date.parse(): Parses a date string and returns the number of milliseconds since the Unix Epoch (January 1, 1970). If the string cannot be parsed, it returns NaN. Date.UTC(): Creates a Date object from UTC values. Date.toString(): Returns a string representation of the Date object in a readable format. valueOf(): Returns the primitive value of the Date object. These methods provide essential functionality for working with dates in JavaScript, enabling developers to efficiently manage and manipulate date values in their applications.  Conclusion The JavaScript Date object is an essential tool for managing datetime in web development. From creating dates to formatting and performing date arithmetic, mastering this object will enable developers to handle time-sensitive data efficiently, regardless of time zone or locale. By using built-in methods and libraries like Moment.js, date-fns, or Day.js, developers can ensure their applications deliver a smooth user experience when working with dates.
15 October 2024 · 8 min to read

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