Source

File: wp-admin/includes/class-custom-image-header.php

public function js_2() {

		?>
<script type="text/javascript">
	function onEndCrop( coords ) {
		jQuery( '#x1' ).val(coords.x);
		jQuery( '#y1' ).val(coords.y);
		jQuery( '#width' ).val(coords.w);
		jQuery( '#height' ).val(coords.h);
	}

	jQuery(document).ready(function() {
		var xinit = <?php echo absint( get_theme_support( 'custom-header', 'width' ) ); ?>;
		var yinit = <?php echo absint( get_theme_support( 'custom-header', 'height' ) ); ?>;
		var ratio = xinit / yinit;
		var ximg = jQuery('img#upload').width();
		var yimg = jQuery('img#upload').height();

		if ( yimg < yinit || ximg < xinit ) {
			if ( ximg / yimg > ratio ) {
				yinit = yimg;
				xinit = yinit * ratio;
			} else {
				xinit = ximg;
				yinit = xinit / ratio;
			}
		}

		jQuery('img#upload').imgAreaSelect({
			handles: true,
			keys: true,
			show: true,
			x1: 0,
			y1: 0,
			x2: xinit,
			y2: yinit,
			<?php
			if ( ! current_theme_supports( 'custom-header', 'flex-height' ) && ! current_theme_supports( 'custom-header', 'flex-width' ) ) {
				?>
			aspectRatio: xinit + ':' + yinit,
				<?php
			}
			if ( ! current_theme_supports( 'custom-header', 'flex-height' ) ) {
				?>
			maxHeight: <?php echo get_theme_support( 'custom-header', 'height' ); ?>,
				<?php
			}
			if ( ! current_theme_supports( 'custom-header', 'flex-width' ) ) {
				?>
			maxWidth: <?php echo get_theme_support( 'custom-header', 'width' ); ?>,
				<?php
			}
			?>
			onInit: function () {
				jQuery('#width').val(xinit);
				jQuery('#height').val(yinit);
			},
			onSelectChange: function(img, c) {
				jQuery('#x1').val(c.x1);
				jQuery('#y1').val(c.y1);
				jQuery('#width').val(c.width);
				jQuery('#height').val(c.height);
			}
		});
	});
</script>
		<?php
	}