How to convert number in specific precision in Javascript

Description

The toPrecision() method returns either the fixed or the exponential representation of a number. This method takes the total number of digits to represent the number as the argument.

Example

var num = 99; 
console.log(num.toPrecision(1)); //"1e+2" 
console.log(num.toPrecision(2)); //"99" 
console.log(num.toPrecision(3)); //"99.0" 
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The code above generates the following result.