I use an example of javascript code:
1 var a = 1; 2 var b = |{}; The cursor is at the position of |( on the character "{" when the cursor shape is block), I find out that I want a should be assigned an object, so I want to modify it like below:
1 var a = {}; So I want to know when cursor is on "{", how to quickly delete all the contents before "{" until the blank after the "=" sign at line 1?
In other normal editors, I'll just press backspace key to delete the code. But I don't how to achieve this in vim.

iand use the backspace key. No body will shoot you for that. I think.eolthen backspace will delete line breaks. You'll also needstartto be included in the setting. (See:help backspace). Don't use this method though! There are several much faster methods detailed in the answers below.