一般来说,这俩单词作"当...的时候"讲时,意思差别不大.
最大的差别就是:while后面的时态必须是进行时的,as范围广一些.
还有一个差别就是:while作"当...的时候"讲时,后面可以接从句也可以接短语,as必须接从句,如果接了短语,就不再是"当...的时候"的意思了.
for example,you can say"She always smiles while talking to her boyfriend"or"She always smiles while she is talking to her boyfriend".
拿as来说,"当他还是个孩子时"可以用"as he was a child",但不可以说"as a child"