Avoid unnecessary getBoundingClientRect() calls

[rattuscz]

May seem like useless micro optimization, but just with this simple change my sizable graph redraw went from 6s to 3s.
Each call to getBoundingClientRect() causes forced layout, avoiding when possible can make big difference.

Details

Avoids getBoundingClientRect() call until actually needed - paths that don't need it will not call this function

[coveralls]

Changes Unknown when pulling 07c9300 on rattuscz:patch-1 into ** on naver:master**.

[netil]

It's okay for getXForText(), but for getYForText(), getBoundingClientRect() are called multiple times.
The height value would be gotten from the above if the execution condition is met.

How about defining an inner function, which get the height calling getBoundingClientRect() just once?

	getYForText(points, d, textElement) {
		const $$ = this;
		let yPos;
		let getHeight = () => {
			const height = textElement.getBoundingClientRect().height;

			getHeight = () => height;
			return height;
		};
		
		if ($$.config.axis_rotated) {
			yPos = (points[0][0] + points[2][0] + getHeight() * 0.6) / 2;
		} else {
			...
		}
		
		// show labels regardless of the domain if value is null
		if (d.value === null && !$$.config.axis_rotated) {
			if (yPos < getHeight()) {
				yPos = getHeight();
				
		..

[netil]

@rattuscz nice work!

BTW, we have some commit format style guideline for the contribution.

• https://github.com/naver/billboard.js/blob/master/CONTRIBUTING.md

[rattuscz]

@netil for getYForText - the conditions on the ifs actually make multiple calls impossible ( if i checked correctly ) - there is no value for which the function is called twice even without any memoize function

• $$.config.axis_rotated
• (d.value < 0 || (d.value === 0 && !$$.hasPositiveValue))
• d.value === null && !$$.config.axis_rotated

the only place was the last if that's why i've used boxHeight variable.

will check the contrib guideline and update, missed it :-)

[netil]

@rattuscz yeah, you're right. The condition doesn't met to be called multiple times.
Plz, check commit format and linting. I'll merge PR If there's no issue. thanks.

[coveralls]

Changes Unknown when pulling 6af4989 on rattuscz:patch-1 into ** on naver:master**.

[netil]

Thanks @rattuscz for your contribution!