function getDiff( pageName, pageContent ) {
		var api = new mw.Api();

		return api.post( {
			action: 'query',
			prop: 'revisions',
			rvprop: 'content',
			rvlimit: '1',
			titles: pageName,
			rvdifftotext: pageContent
		} ).then( function ( data ) {
			var obj;
			for ( var page in data.query.pages ) {
				obj = data.query.pages[ page ];
			}

			var diff;
			if ( obj !== undefined ) {
				diff = obj.revisions[ 0 ].diff[ '*' ];
			}

			return diff;
		} );
	}

{
	"batchcomplete": "",
	"warnings": {
		"main": {
			"*": "Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/postorius/lists/mediawiki-api-announce.lists.wikimedia.org/> for notice of API deprecations and breaking changes. Use [[Special:ApiFeatureUsage]] to see usage of deprecated features by your application."
		},
		"revisions": {
			"*": "The parameter \"rvdifftotext\" has been deprecated.\nBecause \"rvslots\" was not specified, a legacy format has been used for the output. This format is deprecated, and in the future the new format will always be used."
		}
	}
}

rvdifftotext
    Deprecated.

    Use action=compare instead. Text to diff each revision to. Only diffs a limited number of revisions. Overrides rvdiffto. If rvsection is set, only that section will be diffed against this text.