ilyalesik / babel-order-showcase

Babel order showcase

The case shows that order of plugin is doesnt matter.

Suppose we have some code:

var a = 1;

There are two plugins: pluginAtoB and pluginAtoC. pluginAtoB transform the code to

var b = 1;

pluginAtoC transform the code to

var c = 1;

But what happens, if we set pluginAtoB and pluginAtoC both?

{
    plugins: [pluginAtoB, pluginAtoC]
}

In this case oder of plugins at config doesnt matter, always will be

var b = 1;

Why? Plugin pluginAtoB visit Identifier node, while pluginAtoC visit VariableDeclarator node. VariableDeclarator node is upper at AST that Identifier node. Traverse algorithm firstly will find VariableDeclarator and change a to c. Then will find Identifier and change c to b.