JavaScript: Convert a number in bytes to a human-readable string

JavaScript fundamental (ES6 Syntax): Exercise-163 with Solution

Write a JavaScript program to convert a number in bytes to a human-readable string.

Note: Use an array dictionary of units to be accessed based on the exponent.

• Use an array dictionary of units to be accessed based on the exponent.
• Use Number.prototype.toPrecision() to truncate the number to a certain number of digits.
• Return the prettified string by building it up, taking into account the supplied options and whether it is negative or not.
• Omit the second argument, precision, to use a default precision of 3 digits.
• Omit the third argument, addSpace, to add space between the number and unit by default.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2
const prettyBytes = (num, precision = 3, addSpace = true) => {
const UNITS = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
if (Math.abs(num) < 1) return num + (addSpace ? ' ' : '') + UNITS[0];
const exponent = Math.min(Math.floor(Math.log10(num < 0 ? -num : num) / 3), UNITS.length - 1);
const n = Number(((num < 0 ? -num : num) / 1000 ** exponent).toPrecision(precision));
return (num < 0 ? '-' : '') + n + (addSpace ? ' ' : '') + UNITS[exponent];
};
console.log(prettyBytes(1000));
console.log(prettyBytes(-27145424323.5821, 5));
console.log(prettyBytes(123456789, 3, false));

Sample Output:

1 KB
-27.145 GB
123MB

Pictorial Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-163-1 by w3resource (@w3resource) on CodePen.

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JavaScript: Tips of the Day

Checking if a key exists in a JavaScript object?

Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?

var obj = { key: undefined };
obj["key"] !== undefined // false, but the key exists!

You should instead use the in operator:

"key" in obj // true, regardless of the actual value

If you want to check if a key doesn't exist, remember to use parenthesis:

!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj   // ERROR!  Equivalent to "false in obj"

Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:

obj.hasOwnProperty("key") // true

Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined? var obj = { key: undefined }; obj["key"] !== undefined // false, but the key exists! You should instead use the in operator: "key" in obj // true, regardless of the actual value If you want to check if a key doesn't exist, remember to use parenthesis: !("key" in obj) // true if "key" doesn't exist in object !"key" in obj // ERROR! Equivalent to "false in obj" Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty: obj.hasOwnProperty("key") // true For performance comparison between the methods that are in, hasOwnProperty and key is undefined.

Ref: https://bit.ly/2CFNp1X