Can anyone recommend reading for the web-related Javascript "API" so that when Javascript is used in the form of generated code, e.g., through asm.js, the "API"

Can anyone recommend reading for the web-related Javascript "API" so that when Javascript is used in the form of generated code, e.g., through asm.js, the "API" can be used by the "generating program" without the need to learn all of Javascript. Essentially so you could do HTML/CSS/some-other-language (using asm.js, emscripten, or some similar technology) instead of HTML/CSS/JS.