function computeStyle()

in static/js/popper.js [1215:1312]
65 lines of code
13 McCabe index (conditional complexity)

  function computeStyle(data, options) {
    var x = options.x,
      y = options.y;
    var popper = data.offsets.popper;

    // Remove this legacy support in Popper.js v2

    var legacyGpuAccelerationOption = find(data.instance.modifiers, function (modifier) {
      return modifier.name === 'applyStyle';
    }).gpuAcceleration;
    if (legacyGpuAccelerationOption !== undefined) {
      console.warn('WARNING: `gpuAcceleration` option moved to `computeStyle` modifier and will not be supported in future versions of Popper.js!');
    }
    var gpuAcceleration = legacyGpuAccelerationOption !== undefined ? legacyGpuAccelerationOption : options.gpuAcceleration;

    var offsetParent = getOffsetParent(data.instance.popper);
    var offsetParentRect = getBoundingClientRect(offsetParent);

    // Styles
    var styles = {
      position: popper.position
    };

    // Avoid blurry text by using full pixel integers.
    // For pixel-perfect positioning, top/bottom prefers rounded
    // values, while left/right prefers floored values.
    var offsets = {
      left: Math.floor(popper.left),
      top: Math.round(popper.top),
      bottom: Math.round(popper.bottom),
      right: Math.floor(popper.right)
    };

    var sideA = x === 'bottom' ? 'top' : 'bottom';
    var sideB = y === 'right' ? 'left' : 'right';

    // if gpuAcceleration is set to `true` and transform is supported,
    //  we use `translate3d` to apply the position to the popper we
    // automatically use the supported prefixed version if needed
    var prefixedProperty = getSupportedPropertyName('transform');

    // now, let's make a step back and look at this code closely (wtf?)
    // If the content of the popper grows once it's been positioned, it
    // may happen that the popper gets misplaced because of the new content
    // overflowing its reference element
    // To avoid this problem, we provide two options (x and y), which allow
    // the consumer to define the offset origin.
    // If we position a popper on top of a reference element, we can set
    // `x` to `top` to make the popper grow towards its top instead of
    // its bottom.
    var left = void 0,
      top = void 0;
    if (sideA === 'bottom') {
      // when offsetParent is <html> the positioning is relative to the bottom of the screen (excluding the scrollbar)
      // and not the bottom of the html element
      if (offsetParent.nodeName === 'HTML') {
        top = -offsetParent.clientHeight + offsets.bottom;
      } else {
        top = -offsetParentRect.height + offsets.bottom;
      }
    } else {
      top = offsets.top;
    }
    if (sideB === 'right') {
      if (offsetParent.nodeName === 'HTML') {
        left = -offsetParent.clientWidth + offsets.right;
      } else {
        left = -offsetParentRect.width + offsets.right;
      }
    } else {
      left = offsets.left;
    }
    if (gpuAcceleration && prefixedProperty) {
      styles[prefixedProperty] = 'translate3d(' + left + 'px, ' + top + 'px, 0)';
      styles[sideA] = 0;
      styles[sideB] = 0;
      styles.willChange = 'transform';
    } else {
      // othwerise, we use the standard `top`, `left`, `bottom` and `right` properties
      var invertTop = sideA === 'bottom' ? -1 : 1;
      var invertLeft = sideB === 'right' ? -1 : 1;
      styles[sideA] = top * invertTop;
      styles[sideB] = left * invertLeft;
      styles.willChange = sideA + ', ' + sideB;
    }

    // Attributes
    var attributes = {
      'x-placement': data.placement
    };

    // Update `data` attributes, styles and arrowStyles
    data.attributes = _extends({}, attributes, data.attributes);
    data.styles = _extends({}, styles, data.styles);
    data.arrowStyles = _extends({}, data.offsets.arrow, data.arrowStyles);

    return data;
  }