JS: Number.prototype.toPrecision

By Xah Lee. Date: 2017-03-28. Last updated: 2020-09-12.

number.toPrecision(precision): Return a string representation of number, with n significant digits. Result may be in exponential notation. e.g. "1e+1" meaning 1*10^1, or 10. If precision is undefined, call ToString instead.

const num = 3.123;
console.log( num.toPrecision ( 1 ) === "3" ); // true
console.log( num.toPrecision ( 2 ) === "3.1" ); // true
console.log( num.toPrecision ( 3 ) === "3.12" ); // true
console.log( num.toPrecision ( 4 ) === "3.123" ); // true
console.log( num.toPrecision ( 5 ) === "3.1230" ); // true

const num = 12.345;
console.log( num.toPrecision ( 1 ) === "1e+1" ); // true
console.log( num.toPrecision ( 2 ) === "12" ); // true
console.log( num.toPrecision ( 3 ) === "12.3" ); // true

const num = 0.123;
console.log( num.toPrecision ( 1 ) === "0.1" ); // true
console.log( num.toPrecision ( 2 ) === "0.12" ); // true
console.log( num.toPrecision ( 3 ) === "0.123" ); // true

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