Subtitles not displayed on IE11 from v2.6.4 onwards

[davemevans]

Environment

• The MPD passes the DASH-IF Conformance Tool on http://dashif.org/conformance.html
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream
• The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• The issue occurs in the latest reference client on http://reference.dashif.org/dash.js/ and not just on my page

• Link to playable MPD file: https://media.axprod.net/TestVectors/v7-Clear/Manifest_1080p.mpd
• Dash.js version: nightly
• Browser name/version: IE11
• OS name/version: Win10

Steps to reproduce

1. Load a manifest with text. Happens every time.

Observed behaviour

An exception is thrown when appending the init segment because a method in TextController calls Array.prototype.findIndex which is not available in IE11 and not provided by our transcompiler.

Console output

[121528] Streaming Initialized 
[121542] Playback Initialized 
[133680] Parsing complete: ( xml2json: 125ms, objectiron: 11.4ms, total: 0.137s) 
[133767] MediaSource attached to element.  Waiting on open... 
[133769] Manifest has been refreshed at Fri Mar 23 2018 17:04:40 GMT+0800 (中国标准时间)[1521795880.226]  
[133782] MediaSource is open! 
[133783] Duration successfully set to: 734 
[133784] Added 0 inline events 
[133819] video codec: video/mp4;codecs="avc1.640015" 
[133829] AbrController (video) switch from 0 to 1/4 (buffer: 0) . 
[133861] audio codec: audio/mp4;codecs="mp4a.40.2" 
[133863] audio codec: audio/mp4;codecs="mp4a.40.2" 
[133865] audio codec: audio/mp4;codecs="mp4a.40.2" 
[133869] No text data. 
[133879] No embeddedText data. 
[133880] No muxed data. 
[133880] No image data. 
[134228] DRM: KeySystem Access Granted (com.microsoft.playready)!  Selecting key system... 
[154890] DRM: Session created.  SessionID = Error 
[154897] DRM: KeySystem Access Granted 
[154900] DRM: Session created.  SessionID = Error 
[154930] [ScheduleController][ video ] start 
[154936] [ScheduleController][ audio ] start 
[154939] [ScheduleController][ fragmentedText ] start 
[154941] Start Event Controller 
[154947] Native video element event: play 
[154956] [StreamController][onPlaybackStarted] 
[154964] Native video element event: waiting 
[155006] AbrController (video) stay on 1/4 (buffer: 0) 
[155007] ScheduleController - video - quality has changed, get init request for representationid = 2 
[155009] [ScheduleController][ video ] isFragmentProcessingInProgress is already equal to true 
[155014] AbrController (audio) stay on 0/0 (buffer: 0) 
[155015] ScheduleController - audio - quality has changed, get init request for representationid = 10 
[155016] [ScheduleController][ audio ] isFragmentProcessingInProgress is already equal to true 
[155032] ScheduleController - fragmentedText - quality has changed, get init request for representationid = 11 
[155033] [ScheduleController][ fragmentedText ] isFragmentProcessingInProgress is already equal to true 
[155520] Init fragment finished loading saving to fragmentedText's init cache 
[155521] Append Init fragment fragmentedText  with representationId: 11  and quality: 0 
[155540] SourceBuffer append failed "TypeError: Object does not support "findIndex" property or method
[155541] [ScheduleController][ fragmentedText ] - onFragmentLoadingCompleted

This used to work in 2.6.3, and was introduced by 44bb150