Use our own startsWith, which works on IE (#4619)
Use our own startsWith, which works on IE (#4619)


Microsoft/pxt,switchinnovations/pxt,playi/pxt,playi/pxt,switch-education/pxt,Microsoft/pxt,switchinnovations/pxt,Microsoft/pxt,switch-education/pxt,playi/pxt,Microsoft/pxt,Microsoft/pxt,playi/pxt,switch-education/pxt,switchinnovations/pxt,switchinnovations/pxt,switch-education/pxt,switch-education/pxt