How do you round to one decimal place in JavaScript?

Deep dive into rounding methods in JavaScript

It's time to unpack our JavaScript toolkit and explore various options for tackling our rounding task:

The simple path: Math.round() with scaling

Scale your numbers up by the power of tens equivalent to the desired decimal places, then round off and scale down. A simple, yet effective solution.

const roundOneDecimal = num => Math.round(num * 10) / 10; // Where did the zero go? '1 ÷ 10' sent it on vacation.
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Champion of consistency: toFixed()

If consistency is your beat, then the toFixed() method is your rhythm. Giving it a '1' ensures one decimal place, even for whole numbers:

console.log((2.345).toFixed(1)); // "2.3" — nice!
console.log((2).toFixed(1)); // "2.0" — and, it never forgets the .0
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Remember: toFixed() is a string enthuasiast, so switch types when mathematical operations loom:

const toNumber = parseFloat((2.345).toFixed(1)); // 2.3, a number to reckon with.
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For the control freaks: A custom round function

In JavaScript, we are free to build our own round function. With Math.pow(), we can easily adjust the precision of our function:

const customRound = (num, decimals) => {
  const factor = Math.pow(10, decimals);
  return Math.round(num * factor) / factor;  // Because who doesn't like tailoring their own wardrobe?
};
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Guard rails: Managing edge cases and negative numbers

Watch out for bankers' rounding and negative numbers. Remember to be mindful of your math:

const roundNegative = num => -Math.round(-num * 10) / 10;  // Did I hear someone say 'Recycling?'
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Library to the rescue: lodash

Meet _round, part of the versatile lodash library. It doesn't discriminate; positive, negative — it's all just numbers.

const rounded = _.round(2.345, 1); // Everyone deserves some TLC. Even numbers.
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Precision pitfalls and solutions

Multiplying by ten might seem like a good idea until you run into floating-point precision problems. How to fix? Math.pow(), of course:

const rounder = (num, places) => Math.round(num * Math.pow(10, places)) / Math.pow(10, places); // NO PAIN, more gains.
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Which method, when?

Choose the right tool for the job by understanding what each method is best suited for:

Straightforward rounding

• One-off rounding: Number(2.86.toFixed(1))
• Quicker than a sprinter on race day!

Keeping it professional

• Currency: toFixed() to keep those decimal places in sight.
• Fort Knox standard precision.

Data crunching

• Further computations: Use parseFloat() after toFixed().
• Who said we can't have numbers and strings playing nice?

Control freak mode: Precision

• Flexibility: A custom rounding function lets you choose the number of decimal places.
• Precision is the key!

In for the long haul

• Tough customers: For consistent and reliable rounding with both positives and negatives, trust Lodash.
• Never let inconsistency dull your shine!