ansi-mark

🖊️ a highlight marker for your color ansi strings

Before and After

Explanation

If your CLI app outputs strings containing ANSI color codes, like this...

const ansiStr = '\u001b[37m\u001b[33m<\u001b[36mbody\u001b[33m>\u001b[37m            \u001b[39m\n\u001b[37m\t\u001b[33m<\u001b[36mspan\u001b[33m>\u001b[37mGood\u001b[33m</\u001b[36mspan\u001b[33m>\u001b[37m\u001b[39m\n\u001b[37m\t\u001b[33m<\u001b[36mspan\u001b[33m>\u001b[37mBad\u001b[33m<\u001b[36mspan\u001b[33m>\u001b[37m  \u001b[39m\n\u001b[37m\u001b[33m<\u001b[36mbody\u001b[33m>\u001b[37m            \u001b[39m\n\u001b[37m\u001b[39m'
console.log(ansiStr)

... then your ANSI string contains visible, and invisible characters. This makes it difficult if you want to highlight a portion of your string. The start and end position of your highlight needs to account for the invisible characters.

But wouldn't it be simpler for everyone if there was a Node Module that let you highlight a sub-string using the offsets of the visible characters?

That is what ansi-mark does:

const chalk = require('chalk')
 
const opts = {
    start: {line: 3, column: 11},
    end: {line: 4, column: 7},
    color: chalk.bgRed.white.bold,
    resetColor: true
}
 
const result = ansiMark(ansiStr, opts)

Keep Colors

If you want to keep the underlying colors in the portion of the string you are highlighting, use the resetColor: false option:

const chalk = require('chalk')
 
const opts = {
    start: {line: 3, column: 11},
    end: {line: 4, column: 7},
    color: chalk.bgBlack
    resetColor: false
}
 
const result = ansiMark(ansiStr, opts)

Using Offsets

You can also highlight by a linear character offset rather than lines and columns

const chalk = require('chalk')
 
const opts = {
    start: 46,
    end: 64,
    color: chalk.bgRed.white.bold,
    resetColor: true
}
 
const result = ansiMark(ansiStr, opts)

Install

$ yarn add ansi-mark