automatic convert bootstrap v. 3 to bootstrap v. 4 idea ... more on https://github.com/twbs/bootstrap/blob/v4-dev/docs/4.0/migration.md, http://upgrade-bootstrap.bootply.com/

draft.js

let gulp            = require('gulp'),
    replace         = require('gulp-batch-replace'),
    filesExist      = require('files-exist');

gulp.task('bt4', () =>
{
    let diff = {

        '@media (min-width: $screen-xs-min) and (max-width: $screen-sm-max)': '@media (min-width: map-get($grid-breakpoints, xs)) and (max-width: map-get($grid-breakpoints, xs))',
        '@media (min-width: $screen-xs) and (max-width: ($screen-md-min - 1))': '@media (min-width: map-get($grid-breakpoints, xs)) and (max-width: map-get($grid-breakpoints, md)-1)',
        '@media (min-width: $screen-sm-min) and (max-width: $screen-sm-max)': '@include media-breakpoint-only(md)',
        
        '@media (min-width: $screen-xs-min)':       '@include media-breakpoint-up(xs)',
        '@media (min-width: $screen-sm)':           '@include media-breakpoint-up(md)',
        '@media (min-width: $screen-sm-min)':       '@include media-breakpoint-up(md)',
        '@media (min-width: $screen-md-min)':       '@include media-breakpoint-up(md)',
        '@media (min-width: $screen-md)':           '@include media-breakpoint-up(md)',
        '@media (min-width: $screen-md-max)':       '@include media-breakpoint-up(md)',
        '@media (min-width: $screen-lg-min)':       '@include media-breakpoint-up(lg)',

        '@media (max-width: ($screen-xs-min - 1))': '@include media-breakpoint-down(xs)',
        '@media (max-width: $screen-xs-max)':       '@include media-breakpoint-down(xs)',
        '@media (max-width: ($screen-sm-min - 1))': '@include media-breakpoint-down(md)',
        '@media (max-width: $screen-sm)':           '@include media-breakpoint-down(md)',
        '@media (max-width: $screen-sm-min)':       '@include media-breakpoint-down(md)',
        '@media (max-width: $screen-sm-max)':       '@include media-breakpoint-down(lg)',
        '@media (max-width: $screen-md-max)':       '@include media-breakpoint-down(md)',
        '@media (max-width: $screen-lg-max)':       '@include media-breakpoint-down(lg)',

        '@media (max-width: $screen-xs-min - 1)':   '@include media-breakpoint-down(xs)',
        '@media (max-width: $screen-md-min)':       '@include media-breakpoint-down(md)',
        
        // bootstrap 2
        '@media (max-width: $screen-xxs)':          '@include media-breakpoint-down(xs)',

        '.col-*-offset-*':	        '.offset-*',
        '.col-*-push-*':	        '.order-*-2',
        '.col-*-pull-*':	        '.order-*-1',
        '.panel':	                '.card',
        '.panel-heading':	        '.card-header',
        '.panel-title':             '.card-title',
        '.panel-body':              '.card-body',
        '.panel-footer':	        '.card-footer',
        '.panel-primary':	        '.card.bg-primary.text-white',
        '.panel-success':	        '.card.bg-success.text-white',
        '.panel-info':	            '.card.text-white.bg-info',
        '.panel-warning':	        '.card.bg-warning',
        '.panel-danger':	        '.card.bg-danger.text-white',
        '.well':	                '.card.card-body',
        '.thumbnail':	            '.card.card-body',
        '.list-inline > li':	    '.list-inline-item',
        '.dropdown-menu > li':	    '.dropdown-item',
        '.nav navbar > li':	        '.nav-item',
        '.nav navbar > li > a':	    '.nav-link',
        '.navbar-right':	        '.ml-auto',
        '.navbar-btn':	            '.nav-item',
        '.navbar-fixed-top':        '.fixed-top',
        '.nav-stacked':             '.flex-column',
        '.btn-default':             '.btn-secondary',
        '.img-responsive':          '.img-fluid',
        '.img-circle':              '.rounded-circle',
        '.img-rounded':             '.rounded',
        //'.form-horizontal':         '', // @note: removed
        '.radio':                   '.form-check',
        '.checkbox':                '.form-check',
        '.input-lg':                '.form-control-lg',
        '.input-sm':                '.form-control-sm',
        '.control-label':           '.form-control-label',
        '.table-condensed':         '.table-sm',
        '.pagination > li':         '.page-item',
        '.pagination > li > a':     '.page-link',
        //'.item':                     '.carousel-item', // @note: this is too much basic word
        '.text-help':               '.form-control-feedback',
        '.pull-right':              '.float-right',
        '.pull-left':               '.float-left',
        '.center-block':            '.mx-auto',
        '.hidden-xs':               '.d-none',
        '.hidden-sm':               '.d-sm-none',
        '.hidden-md':               '.d-md-none',
        '.visible-xs':              '.d-block.d-sm-none',
        '.visible-sm':              '.d-block.d-md-none',
        '.visible-md':              '.d-block.d-lg-none',
        '.visible-lg':              '.d-block.d-xl-none',
        '.label':                   '.badge',
        '.badge':                   '.badge.badge-pill',
        
        // twig
        
        'col-xs-':                  'col-',
        'col-md-':                  'col-lg-',
        'col-sm-':                  'col-md-'
    };

    let replaceThis = [];
    Object.keys(diff).forEach(function(key)
    {
        replaceThis.push([key, diff[key]]);
    });

    return gulp
        .src(filesExist('./scss/**'))
        .pipe(replace(replaceThis))
        .pipe(gulp.dest('./build/scss'));
});

Conversion is not correct.
Reason: sm in Bootstrap 4 is now md.
Example: @media (min-width: $screen-sm) is now @include media-breakpoint-up(md) for same screen width

@devtroll updated, thanks

@landsman No probs, but i See another logical issue. "screen-sm-max" means maximum width of 992px. So i think it should be media-breakpoint-down(lg) instead of media-breakpoint-down(md). Do you agree with that?

Yes this is my scenario as well.. replacing templates or updating existing projects

Just to clarify, I am not having the templates rewritten dynamically every time on the frontend, that would indeed be overkill. It is converting the HTML templates programmatically on my machine once via a gulp task and writes the changes to the files....

Can we adapt the script to Bootstrap 5? https://getbootstrap.com/docs/5.0/migration/

@Bachstelze nope, you have to write your own for 4 to 5 migration.
I am still surprised that these things are not build-in in Bootstrap.

@kerryj89 thanks, but why jQuery? It's little bit outdated today.

No problem! Thanks for your script, also. As for jQuery syntax, it's what https://github.com/creativetimofficial/bootstrap-converter uses (it uses cheerio which they call jQuery for the server, never heard of it until recently). That will be helpful to programmatically rewrite my HTML in more complex scenarios where elements or classes might have moved around. Honestly as outdated as jQuery might be in customer facing sites, the sizzle engine is still a joy to use with how frictionless it is to traverse up and down the DOM. I think it's very applicable for this one time conversion use case.

It doesnt work for angular project though , since angular uses ngTemplates & template binding which are modified by this converter

eg. *ngIf="domains && domains.length>0" converted to *ngif="domains&& domains.length>0" where the conditional clause is altered

@landsman how do i run it though on a project structure with files like
Testapp >> home.ts home.html home.css

@HariPrasad-1493 Really up to you. You can copy paste defined object and write your own replace script. This is just a draft.

@HariPrasad-1493 Really up to you. You can copy paste defined object and write your own replace script. This is just a draft.

Ohk.. thought this was some gulp task i can run even though i haven't used gulp before :)

It doesnt work for angular project though , since angular uses ngTemplates & template binding which are modified by this converter

eg. *ngIf="domains && domains.length>0" converted to *ngif="domains&& domains.length>0" where the conditional clause is altered

I was able to use it on an AngularJS project and it didn't convert to html entity. It wasn't perfect but got 90% right. Maybe this can help: https://stackoverflow.com/a/31574528/3266845 I still looked through each template to make sure. I noticed it would close my attributes (i.e. <span attr-foo>Test</span> would turn into <span attr-foo="">Test</span> and sometimes would get confused by quotes and close prematurely. The worst is when it just removed a chunk of code sneakily, maybe a memory fault.

Sorry for this off-topic-on-topic reply, landsman.