I build a game to webGL type, It can't get json data from php...

Dear all: I design a simple game with unity,when the game start , it will catch json data from a php script first.

It can work on Unity 5.5.1f1 , If I build a exe type, It also can work.

If I build webGL, It can't get the json data from php scrip, why?

Can anybody help me?

Thanks a lot.