code: function createProgressHandler() {
  	const startTime = Date.now();
  	let lastShownBuildingMessageTime = null;
  	let lastUnshownBuildingMessage = null;
  
  	return ( percentage, msg, ...details ) => {
  		const nowTime = Date.now();
  		const timeString = ( ( nowTime - startTime ) / 1000 ).toFixed( 1 ) + 's';
  		const percentageString = `${ Math.floor( percentage * 100 ) }%`;
  		const detailsString = details
  			.map( detail => {
  				if ( ! detail ) {
  					return '';
  				}
  				if ( detail.length > 40 ) {
  					return `…${ detail.substr( detail.length - 39 ) }`;
  				}
  				return detail;
  			} )
  			.join( ' ' );
  		const message = `${ timeString } ${ percentageString } ${ msg } ${ detailsString }`;
  
  		// There are plenty of 'building' messages that make the log too long for CircleCI web UI.
  		// Let's throttle the 'building' messages to one per second, while always showing the last one.
  		if ( msg === 'building' ) {
  			if ( lastShownBuildingMessageTime && nowTime - lastShownBuildingMessageTime < 1000 ) {
  				// less than 1000ms since last message: ignore, but store for case it's the last one
  				lastUnshownBuildingMessage = message;
  				return;
  			}
  
  			// the message will be shown and its time recorded
  			lastShownBuildingMessageTime = nowTime;
  			lastUnshownBuildingMessage = null;
  		} else if ( lastUnshownBuildingMessage ) {
  			// The last 'building' message should always be shown, no matter the timing.
  			// We do that on the first non-'building' message.
  			console.log( lastUnshownBuildingMessage ); // eslint-disable-line no-console
  			lastUnshownBuildingMessage = null;
  		}
  
  		console.log( message ); // eslint-disable-line no-console
  	};
  }
docs: /*
  Create reporter for ProgressPlugin (used with EMIT_STATS)