test.js

function consolidateImageWMSLayers (layers) {
  let i, j

  const layersProcessed = [] // need to record processed layers to only process once
  const layersToConsolidate = [] // intended to contain arrays of layer that are to be consolidated
  const otherIndices = [] // indices of unconsolidated layers, will be used when assembling new layers

  const isImageWMS = layer => layer.type === 'Image' && layer.source.type === 'ImageWMS'
  const isProcessed = layer => layersProcessed.indexOf(layer) !== -1
  const isCandidate = (l1, l2) => l1.source.url === l2.source.url && !(l1.metadata.unconsolidated === true || l2.metadata.unconsolidated === true)

  // find all ImageWMS layers with same URL to fill above arrays
  for (i = 0; i < layers.length; i++) {
    if (!isImageWMS(layers[i])) {
      otherIndices.push(i)
    } else if (!isProcessed(layers[i])) {
      const layersMatched = []
      let layerIndex = 0
      for (j = 0; j < layers.length; j++) {
        if (isImageWMS(layers[j]) && !isProcessed(layers[j]) && isCandidate(layers[i], layers[j]) && (layersMatched.length === 0 || layerIndex === j - 1)) {
          layersMatched.push(layers[j])
          layerIndex = j
          layersProcessed.push(layers[j])
        }
      }
      if (layersMatched.length > 1) {
        layersToConsolidate.push(layersMatched)
      } else {
        otherIndices.push(i)
      }
      layersProcessed.push(layers[i])
    }
  }
}