1 files changed, 50 insertions, 0 deletions
diff --git a/app/assets/javascripts/behaviors/gl_emoji/spread_string.js b/app/assets/javascripts/behaviors/gl_emoji/spread_string.js
new file mode 100644
index 00000000000..2380349c4fa
--- /dev/null
+++ b/app/assets/javascripts/behaviors/gl_emoji/spread_string.js
@@ -0,0 +1,50 @@
+// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charCodeAt#Fixing_charCodeAt()_to_handle_non-Basic-Multilingual-Plane_characters_if_their_presence_earlier_in_the_string_is_known
+function knownCharCodeAt(givenString, index) {
+  const str = `${givenString}`;
+  const end = str.length;
+
+  const surrogatePairs = /[\uD800-\uDBFF][\uDC00-\uDFFF]/g;
+  let idx = index;
+  while ((surrogatePairs.exec(str)) != null) {
+    const li = surrogatePairs.lastIndex;
+    if (li - 2 < idx) {
+      idx += 1;
+    } else {
+      break;
+    }
+  }
+
+  if (idx >= end || idx < 0) {
+    return NaN;
+  }
+
+  const code = str.charCodeAt(idx);
+
+  let high;
+  let low;
+  if (code >= 0xD800 && code <= 0xDBFF) {
+    high = code;
+    low = str.charCodeAt(idx + 1);
+    // Go one further, since one of the "characters" is part of a surrogate pair
+    return ((high - 0xD800) * 0x400) + (low - 0xDC00) + 0x10000;
+  }
+  return code;
+}
+
+// See http://stackoverflow.com/a/38901550/796832
+// ES5/PhantomJS compatible version of spreading a string
+//
+// [...'foo'] -> ['f', 'o', 'o']
+// [...'🖐🏿'] -> ['🖐', '🏿']
+function spreadString(str) {
+  const arr = [];
+  let i = 0;
+  while (!isNaN(knownCharCodeAt(str, i))) {
+    const codePoint = knownCharCodeAt(str, i);
+    arr.push(String.fromCodePoint(codePoint));
+    i += 1;
+  }
+  return arr;
+}
+
+module.exports = spreadString;