diff_kit

Deno lib that compares 2 strings and generates result like assertEquals(), also in HTML.

Example

// To download and run this example:
// curl 'https://raw.githubusercontent.com/jeremiah-shaulov/diff_kit/v2.0.2/README.md' | perl -ne '$y=$1 if /^```(ts\\b)?/;  print $_ if $y&&$m;  $m=$y&&($m||m~^// deno .*?/example1.ts~)' > /tmp/example1.ts
// deno run /tmp/example1.ts

import {diff, DiffText, DiffTerm, DiffHtml} from 'https://deno.land/x/diff_kit@v2.0.2/mod.ts';

const left =
`abc
def
`;
const right =
`abc
de*f
`;

console.log('--- Default (terminal colors) ---');
let result = diff(left, right);
console.log(result);

console.log('--- Plain text ---');
result = diff(left, right, new DiffText({indentWidth: 2}));
console.log(result);

console.log('--- Terminal colors ---');
result = diff(left, right, new DiffTerm({indentWidth: 2}));
console.log(result);

console.log('--- HTML ---');
result = diff(left, right, new DiffHtml({indentWidth: 2}));
console.log(result);

Screenshot

diff()

The main function that this module exports is called diff().

interface DiffSubj
{	readonly length: number;
    charCodeAt(i: number): number;
    slice(from: number, to: number): string;
}

function diff(left: DiffSubj, right: DiffSubj, diffHandler: DiffHandler=new DiffTerm({indentWidth: 4})): string

DiffSubj interface is string-compatible, and the most usual use case is to pass strings to the diff() function.

How the result is generated

The 3rd parameter of diff() is of DiffHandler type. DiffHandler has exactly this implementation:

class DiffHandler
{	left: DiffSubj = '';
    right: DiffSubj = '';

    posLeft = 0;
    posRight = 0;

    protected result = '';

    addEqual(endPosLeft: number)
    {	this.result += this.left.slice(this.posLeft, endPosLeft);
    }

    addDiff(endPosLeft: number, endPosRight: number)
    {	if (endPosRight > this.posRight)
        {	this.result += '[-]';
            this.result += this.right.slice(this.posRight, endPosRight);
        }
        if (endPosLeft > this.posLeft)
        {	this.result += '[+]';
            this.result += this.left.slice(this.posLeft, endPosLeft);
        }
        this.result += '[=]';
    }

    toString()
    {	return this.result;
    }
}

When an instance of DiffHandler is used as a parameter to diff(), the very basic plain text diff is generated: deleted parts will be marked with [-]...[=], inserted parts with [+]...[=], and changed parts with [-]...[+]...[=].

// To download and run this example:
// curl 'https://raw.githubusercontent.com/jeremiah-shaulov/diff_kit/v2.0.2/README.md' | perl -ne '$y=$1 if /^```(ts\\b)?/;  print $_ if $y&&$m;  $m=$y&&($m||m~^// deno .*?/example2.ts~)' > /tmp/example2.ts
// deno run /tmp/example2.ts

import {diff, DiffHandler} from 'https://deno.land/x/diff_kit@v2.0.2/mod.ts';

const left =
`abc
def
`;
const right =
`abc
de*f
`;

console.log(diff(left, right, new DiffHandler));

Result:

abc
de[-]*[=]f

diff() calls the following methods and properties of DiffHandler to produce the result:

left and right properties are set to the first and the second diff() parameter.
addEqual(endPosLeft: number) is called to add a text part that is the same for both the left-hand and the right-hand sides of the diff. this.posLeft contains the starting index of the part, and endPosLeft is the end index, so to extract the part do: this.left.slice(this.posLeft, endPosLeft).
addDiff(endPosLeft: number, endPosRight: number) is called to add a part that is different. The left part is this.left.slice(this.posLeft, endPosLeft), and the right is this.right.slice(this.posRight, endPosRight). One of the parts can be empty (but not both).
Before calling addEqual() and addDiff(), posLeft and posRight properties are set to current positions in the left and right.
toString() - at last, the object is converted to string to produce the result.

The same method is not called twice in sequence. That is, for example, after addEqual() either addDiff() or toString() will be called.

To produce results in different formats, use subclasses of DiffHandler that have different implementations of addEqual() and addDiff().

This library contains 3 classes that provide visualization of the diff result:

DiffText - generates line-by-line comparison in plain text.
DiffTerm - generates line-by-line comparison with highlighting different parts using terminal colors. This is very similar to standard assertEquals() function.
DiffHtml - like the previous, but generates HTML.

All these classes provide option to adjust colors and markup:

class DiffText extends DiffHandler
{	constructor(options?: DiffTextOptions, styles?: DiffTextStyles);
}
class DiffTerm extends DiffText
{	constructor(options?: DiffTextOptions, styles?: DiffTextStyles);
}
class DiffHtml extends DiffText
{	constructor(options?: DiffTextOptions, styles?: DiffTextStyles);
}

interface DiffTextOptions
{	/**	Number of spaces to be used as indent: from 0 to 10 (inclusive), or -1 for TAB.
     **/
    indentWidth?: number;
}

interface DiffTextStyles
{	/**	What to insert before "-" char that denotes line deletion. Like `<b style="color:red">`
     **/
    minusBegin?: string;

    /**	What to insert after "-" char that denotes line deletion. Like `</b>`
     **/
    minusEnd?: string;

    /**	What to insert before "+" char that denotes line insertion. Like `<b style="color:green">`
     **/
    plusBegin?: string;

    /**	What to insert after "+" char that denotes line insertion. Like `</b>`
     **/
    plusEnd?: string;

    /**	What to insert in the beginning of deleted line. Like `<span style="color:red">`
     **/
    deletedLightBegin?: string;

    /**	What to insert in the end of deleted line. Like `</span>`
     **/
    deletedLightEnd?: string;

    /**	What to insert in the beginning of inserted line. Like `<span style="color:green">`
     **/
    insertedLightBegin?: string;

    /**	What to insert in the end of inserted line. Like `</span>`
     **/
    insertedLightEnd?: string;

    /**	What to insert where actual deleted chars on the line are starting. Like `<span style="background-color:red; color:white">`
     **/
    deletedBegin?: string;

    /**	What to insert where actual deleted chars on the line are ending. Like `</span>`
     **/
    deletedEnd?: string;

    /**	What to insert where actual inserted chars on the line are starting. Like `<span style="background-color:green; color:white">`
     **/
    insertedBegin?: string;

    /**	What to insert where actual inserted chars on the line are ending. Like `</span>`
     **/
    insertedEnd?: string;
}

Extending this library

You can create your own subclass of DiffHandler to generate the result in different form, and use it in your project, or to publish it to deno.land/x. It’s recommended to prefix the library name with diff_kit_ex_.