as-html/index.js

HTML templating with es6 quasi literals.

'use strict'

var escapeHTML = require('escape-html')
module.exports = html

/**
 * Converts a quasi literal to safe html, with support for arrays.
 * Inspired by http://www.2ality.com/2015/01/template-strings-html.html
 *
 * Substitutions are escaped by default but can be raw html if preceded with a bang.
 */
function html (literals /* substitutions... */) {
  // Use raw literal sections: we don’t want
  // backslashes (\n etc.) to be interpreted
  var raw = literals.raw
  var result = ''
  var i
  var len
  var sub
  var lit
  var safe

  for (i = 1, len = arguments.length; i < len; i++) {
    // Retrieve the literal section preceding
    // the current substitution (arguments are offset by 1)
    lit = raw[i - 1]
    // Allow safe html override by prefixing interpolation with a bang.
    // Html is sanitized by default.
    safe = lit[lit.length - 1] === '!'
    sub = normalize(arguments[i], safe)
    if (safe) lit = lit.slice(0, -1)

    result += lit + sub
  }

  // Take care of last literal section
  // (Never fails, because an empty template string
  // produces one literal section, an empty string)
  result += raw[raw.length - 1]

  return result
}

/**
 * Function that normalizes the interpolation substitions.
 * It flattens arrays and ignores nullish and falsey values.
 * Everything else is converted to a string.
 */
function normalize (val, safe) {
  return (
    // Ignore nullish.
    val == null ? ''
    // Ignore false.
    : val === false ? ''
    // Flatten arrays and recursively convert to strings.
    : Array.isArray(val) ? val.map(normalize).join('')
    // Escape all unsafe values by default.
    : safe === false ? escapeHTML(val)
    // Convert a safe value to a string.
    : String(val)
  )
}