JavaScript
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Returns the number of characters in a string
finds the first occurrence from the beginning.
finds the last occurrence from the end.
Extracts from 'start' up to (but not including) 'end'
Similar to slice, but cannot handle negative indexes.
Extracts a 'length' number of characters starting at 'start'.
Convert a string to lowercase.
Convert a string to uppercase.
Remove whitespace from the beginning and end of a string.
Remove whitespace from the beginning of a string.
Remove whitespace from the end of a string.
Combine two or more strings
Replace parts of a string with a new substring
Replace parts of a string with a new substring
Uses regular expressions to search for patterns within a string
split a string to an array
Check if one string exists within another
Check if a string begins with specific characters
Check if a string ends with specific characters
Finds the index of the first occurrence of a substring
Creates a new string by repeating your original string a specified number of times
Add specified char at start
Add specified char at end
Convert other types to number
parses an argument and returns a floating point number
parses a string argument and returns an integer.
formats this number using fixed-point notation.
returns a string representing this number in exponential notation
returns a string with a language-sensitive representation of this number.
returns a string representing this number to the specified precision.
determines if value is a finite number
determines whether the passed value is an integer.
determines whether the passed value is Not a number.
returns the value of this number
turns the input into an object
copies properties from one or more source objects to a target object
creates a new object, using an existing object
useless
useless
returns an array of a given object's own string-keyed property key-value pairs
transforms a list of key-value pairs into an object
returns an object describing the configuration of a specific property on a given object
determines whether two values are the same value
number of elements
returns the item at that index
merge two or more arrays
shallow copies part of this array to another.
new array iterator object that contains the key/value pairs for each index in the array
tests whether all elements in the array pass the test
changes all elements within a range of indices in an array to a static value. It returns the modified array.
filter array by the callbackfn.
find first element by the callbackfn
returns the index of the first element in an array that satisfies the provided testing function.
iterates the array in reverse order and returns the value of the first element that satisfies the provided testing function.
iterates the array in reverse order and returns the index of the first element that satisfies the provided testing function
creates a new array with all sub-array elements concatenated into it recursively up to the specified depth
returns a new array formed by applying a given callback function to each element of the array, and then flattening the result by one level.
executes a provided function once for each array element
creates a new, shallow-copied Array instance from an iterable or array-like object.
creates a new, shallow-copied Array instance from an async iterable, iterable, or array-like object.
determines whether an array includes a certain value among its entries, returning true or false
returns the first index at which a given element can be found in the array, or -1 if it is not present.
determines whether the passed value is an Array.
creates and returns a new string by concatenating all of the elements in this array, separated by commas or a specified separator string
instances returns a new array iterator object that contains the keys for each index in the array.
returns the last index at which a given element can be found in the array, or -1 if it is not present. The array is searched backwards, starting at fromIndex.
creates a new array populated with the results of calling a provided function on every element in the calling array
creates a new Array instance from a variable number of arguments, regardless of number or type of the arguments
removes the last element from an array and returns that element. This method changes the length of the array
adds the specified elements to the end of an array and returns the new length of the array.
combines array elements into one value using a provided function
combines array elements (right-to-left) into a single value.
reverses the order of elements within an array, modifying it directly.
removes the first array element and returns it
extracts a portion of an array into a new array, leaving the original unchanged
method tests if at least one array element matches a provided condition.
rearranges array elements in place, typically in ascending order.
method directly modifies an array by removing, replacing, or adding elements
method formats array elements into a localized string with separators.
method creates a new array with elements in reversed order, leaving the original array unchanged
method creates a sorted copy of an array without modifying the original
creates a new array after removing/replacing elements, leaving the original array unchanged
converts an array into a comma-separated string.
method adds elements to the start of an array and returns the new length
provides an iterator for an array's values
creates a copy of an array, replacing the element at a specified index with a new value
returns the day of the month for this date according to local time.
returns the day of the week for this date
returns the year for this date
returns the hours for this date
returns the milliseconds for this date
returns the minutes for this date
returns the month for this date
returns the seconds for this date
returns the number of milliseconds for this date since the epoch
returns the difference, in minutes
returns the day of the month for this date (universal time)
returns the day of the week for this date (universal time)
returns the year for this date (universal time)
returns the hours for this date (universal time)
returns the milliseconds for this date (universal time)
returns the minutes for this date (universal time)
returns the month for this date (universal time)
returns the seconds in the specified date (universal time)
returns the number of milliseconds elapsed since the epoch
parses a string representation of a date, and returns the date's timestamp
changes the day of the month for this
changes the year, month, and/or day of month for this date
modifies a date object's hours/time based on local time
changes the milliseconds for this date
changes the minutes for this date
changes the month and/or day of the month for this date
changes the seconds and/or milliseconds for this date
changes the timestamp for this date
changes the day of the month for this date UTC
changes the year for this date UTC
changes the hours, minutes, seconds, and/or milliseconds for this date
changes the milliseconds for this date UTC
changes the minutes for this date UTC
changes the month and/or day of the month for this date UTC
changes the seconds and/or milliseconds for this date
returns a string representing the date
returns a string in the date time string format
returns a string ISO format
formats a date according to the user's locale
provides a locale-aware date/time representation
returns a locale-sensitive time string
returns a string representing this date
returns a string representing the time portion of this date
converts a date to a UTC-formatted string (RFC 7231)
returns a timestamp in milliseconds, treating input as UTC
returns a date's primitive representation as milliseconds
Anchor element
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Predictable, always produce the same output for the same input. No side effects (modifying external state, network requests, etc.). Easier to reason about and test.
Can have side effects
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Changing global variables Interacting with the DOM Performing I/O operations (files, network) Generating random numbers
Can have side effects
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Small, focused functions that encapsulate specific tasks. Improve readability and maintainability.
Can have side effects
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Respond to user interactions (clicks, form submissions, etc.) or system events. Often change application state or trigger updates.
Can have side effects
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Handle operations that take time to complete (network requests, timers). Use promises or the async/await syntax for cleaner handling of results.
Can have side effects
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Take other functions as arguments or return them as results. Powerful for abstraction and functional programming patterns. Examples: map (applies a function to each element of an array) filter (creates a new array with elements that pass a condition) reduce (aggregates array values into a single value)