Javascript - 创建打印到HTML功能不起作用

I am trying to create a "printf" function that will take in input 'x' and output the resulting data to print inside of a 'p' tag with an 'id' of 'para'. But I can't seem to figure out why it isn't working. I don't know if I should use 'this' in conjunction with 'x'. But I don't know.I am trying to create a "printf" function that