Modern JavaScript Web Development Cookbook

Padding strings 

You can pad a string to a given length by adding repeated strings either at the left or at the right of the original text by using .padStart(...) and .padEnd(...):

"Hello".padStart(12);       // "       Hello""Hello".padStart(12,"XYZ"); // "XYZXYZXHello""Hello".padStart(3);        // "Hello"; no effect here "Hello".padEnd(12);         // "Hello       ""Hello".padEnd(12,"XYZ");   // "HelloXYZXYZX""Hello".padEnd(4);          // "Hello"; no effect here either

Among possible uses, you may pad a number with zeroes to the left. We have to transform the number into a string because the padding methods are only available for strings:

let padded = String(229.6).padStart(12, "0"); // "0000000229.6"

The reason for using padStart and padEnd instead of padLeft and padRight has ...