JavaScript has many different built-in functions which ease the process of coding. Built-in functions are pre-coded functions that are readily available to use in one's project. 

Examples are as below: 

• toExponential() - It displays a number in the form of an exponent 
• toFixed() - Defines the number of digits to the right of a decimal number
• toLocaleString() - Returns the string value of a number 
• toPrecision() - Define the total numbers of a digit to be displayed after the decimal point
• valueOf() - Returns the actual value of a number 
• charAt() - Returns the value of a character at a specific index 
• concat() - Concatenates or appends two strings to produce a new string 
• length() - Returns the total length of a string
• replace() - Replaces parts of a string with the a new string  
• Date() - Return the time and date of today  
• getDate() - Returns the date of the current month in accordance with the local time  
• getDay() - Returns the day of the current week in accordance with the local time  
• getHours() - Returns the hours of the specified day in accordance with the local time  
• getMilliseconds() - Returns the milli seconds of the specified date in accordance with the local time 
• getMinutes() - Returns the minutes of the specified date in accordance with the local time 
• every() - Returns the value to be true if every element present in an array is in accordance with the testing function given
• filter() - Filter out the elements of an array according to the given condition and creates a new array  
• forEach() - Calls the function for every element in the array  
• push() and pop() - To remove and add an element to the index of the array respectively  
• abs() - Provides the absolute value of a number 
• acos() - Provides the arc cosine of the number 

Similarly we have functions like cos(), sin(), tan(), acos(), asin(), atan(), log() and many other mathematical functions.