DEV Community: Pritom Deb

Important string methods

Pritom Deb — Mon, 27 Dec 2021 15:54:55 +0000

1. concat(str1, str2, ... , strN)
The concat() method joins two or more strings. The concat() method does not change the existing strings. The concat() method returns a new string.

2. endsWith(searchString, length)
Checks whether a string ends with specified string/characters. It only returns true or false. The endsWith() method is case sensitive.

3. includes(searchString, position)
Checks whether a string contains the specified string/characters. It only returns true or false. The includes() method is case sensitive.

4. indexOf(searchValue, fromIndex)
Returns the position of the first found occurrence of a specified value in a string. The indexOf() method returns -1 if the value is not found. The indexOf() method is case sensitive.

5. lastIndexOf(searchValue, fromIndex)
Returns the position of the last found occurrence of a specified value in a string. The indexOf() method returns -1 if the value is not found. The lastIndexOf() method is case sensitive.

6. replace(regexp/substr, newSubstr/replacerFunction)
Searches a string for a specified value, or a regular expression, and returns a new string where the specified values are replaced.

7. slice(beginIndex, endIndex)
Extracts a part of a string and returns a new string.

8. split(separator, limit)
Splits a string into an array of substrings. If (" ") is used as separator, the string is split between words.

9. startsWith(searchString, position)
Checks whether a string begins with specified characters. It only returns true or false. The startsWith() method is case sensitive.

10. toLocaleLowerCase()
Converts a string to lowercase letters, according to the host's locale. The locale is based on the language settings of the browser. The toLocaleLowerCase() returns the same result as toLowerCase(), except for locales that conflict with the regular Unicode case mappings (such as Turkish).

11. toLocaleUpperCase()
Converts a string to uppercase letters, according to the host's locale. The locale is based on the language settings of the browser. The toLocaleUpperrCase() returns the same result as toLowerCase(), except for locales that conflict with the regular Unicode case mappings (such as Turkish).

12. toLowerCase()
Converts a string to lowercase letters.

13. toLowerCase()
Converts a string to uppercase letters.

Important Math methods

Pritom Deb — Wed, 22 Dec 2021 20:11:27 +0000

1. Math.min(value0, value1, ... , valueN)
The Math.min( ) method is used to find the lowest value in a list of arguments. Have a look at the example below:

2. Math.max(value0, value1, /* ... ,*/ valueN)
The Math.max( ) method is used to find the highest value in a list of arguments. Have a look at the example below:

3. Math.round(a number value)
The Math.round(x) method returns the value of a number x rounded to its nearest integer:

4. Math.sqrt(a number value)
The Math.sqrt(x) is used to return the square root of a number x. If the value of x is negative, Math.sqrt() returns NaN. Have a look at the example below:

5. Math.pow(base, exponent)
The Math.pow(x, y) returns the value of x to the power of y. If the base is negative and the exponent is not an integer, the result is NaN. Let’s have a look at the below example:

6. Math.floor(a number value)
The Math.floor(x) returns the value of x rounded down to its nearest integer. Math.floor(null) returns 0, not a NaN.

7. Math.random( )
The Math.random() returns a random number between 0 and 1. It’s often used to extract random elements from an array.

8. Math.ceil(a number value)
The Math.ceil(x) returns the value of x rounded up to its nearest integer:

Important array methods

Pritom Deb — Wed, 22 Dec 2021 16:24:26 +0000

1. concat()
Joins two or more arrays, and returns a copy of the joined arrays

the num will return [1, 2, 3, 4, 5, 6]

2. every((element, index, array) => { /* ... */ })
Checks if every element in an array pass a test

teenager will reply true while adult while reply false. The every() method only returns true or false. The every() method does not execute the function for empty elements. Every element has to pass the test for the every() method to work.

3. filter((element, index, array) => { /* ... */ })
Creates a new array with every element in an array that pass a test

adult will return a new array ["18","19","20"]

4. find((element, index, array) => { /* ... */ })
Returns the value of the first element in an array that pass a test

adult will return 18.

5. findIndex((element, index, array) => { /* ... */ })
Returns the index of the first element in an array that pass a test

adult will return 3. Will return -1 if no element matches the condition.

6. forEach((element, index, array) => { /* ... */ })
Calls a function for each array element

adult will return undefined. It is very important to note that forEach only iterate through a array. It doesn't return any value.

7. Array.form(arrayLike, (element, index) => { /* ... */ })
Creates an array from an object

nameArray will return ["p", "r", "i", "t", "o", "m"]

8. includes(searchElement, fromIndex)
Check if an array contains the specified element

adult will return true.

9. indexOf(searchElement, fromIndex)
Search the array for an element and returns its position

adult will return 3. Will return -1 if no element matches the condition.

10. lastIndexOf(searchElement, fromIndex)
Search the array for an element, starting at the end, and returns its position

adult will return 4. Will return -1 if no element matches the condition.

11. map((element, index, array) => { /* ... */ })
Creates a new array with the result of calling a function for each array element

everyone will return [14, 15, 16, 17, 18, 19, 20]

12. pop()
Removes the last element of an array, and returns that element

newAges will return 20. pop() returns the element it removed.

13. push(element0, element1, /* ... ,*/ elementN)
Removes the last element of an array, and returns that element

newAges will return 8. The push() method adds new items to the end of an array. The push() method returns the new length.

14. reduce((previousValue, currentValue, currentIndex, array) => { /* ... */ }, initialValue)
Reduce the values of an array to a single value (going left-to-right)

total will return 10. The reduce() method returns a single value: the function's accumulated result.

15. reduceRight((previousValue, currentValue, currentIndex, array) => { /* ... */ }, initialValue)
Reduce the values of an array to a single value (going right-to-left)

total will return 10. The reduceRight() method returns a single value: the function's accumulated result.

16. reverse()
Reverses the order of the elements in an array

newAges and ages both will return [4, 3, 2, 1]. The reverse() method overwrites the original array.

17. shift()
Removes the first element of an array, and returns that element

newAges will return 1. The shift() method returns the shifted element.

18. slice(start, end)
Selects a part of an array, and returns the new array

newAges will return [1, 2]. The slice() method returns selected elements in an array, as a new array.

19. some((element, index, array) => { /* ... */ } )
Checks if any of the elements in an array pass a test

newAges will return true. The some() method only returns true or false. Only one element has to pass the test for some() method to work.

20. splice(start, deleteCount, item1, item2, itemN )
Adds/Removes elements from an array

newAges will return [15, 16, 17]. ages will return [18, 19, 20]. The splice() method overwrites the original array.

21. toString()
Converts an array to a string, and returns the result

newAges will return "1,2,3,4,5". The toString() method returns a string with array values separated by commas.

22. unshift(element0, element1, /* ... ,*/ elementN)
Adds new elements to the beginning of an array, and returns the new length

newAges will return 6. The unshift() method overwrites the original array.