Very little. The situation in China was more complicated than Chinese vs the invading Japanese.

China was in the middle of a civil war when the japanese invaded, which began in 1927 and didnt end until 1950, with the communists winning mainland China and the nationalists retreated to Taiwan. This is the cause of the political tension between them.

When the Japanese invaded in 1937 (beginning the second sino-japanese war), the second world war had not yet begun.

When the Second World War did get into full swing, the Allies, beginning with the British and later the Americans and Soviets, did provide aid to the Chinese. However this aid mostly went to the nationalists, not the communists, for several reasons. The communists and nationalist did stop fighting for short periods during the sindo-japanese war to unite against the japanese, but this weak alliance came to an end after fighting broke out between the two over control of key regions. The communist side favoured guerrilla tactics against the Japanese, whilst the nationalists preferred more conventional warfare.This meant that the supplies sent by the allies to china usually went to the nationalists, not the communists.

Buss, Claude Albert. [1972] (1972). Stanford Alumni Association. The People's Republic of China and Richard Nixon. United States.