Works fine with Javascript:
atom-text-editor {
text-rendering: optimizeLegibility;
font-family: "Operator Mono";
font-weight: 400;
line-height: 1.7;
}
atom-pane atom-text-editor {
margin-top: 10px;
margin-bottom: 10px;
padding: 0;
}
atom-text-editor::shadow {
.storage.type.function.arrow,
.keyword.operator,
.meta.brace {
font-family: "Fira Code";
}
.string.quoted,
.string.regexp {
-webkit-font-feature-settings: "liga" off, "calt" off;
}
}- Save. It's done.



Operator Mono: http://www.typography.com/blog/introducing-operator ($100)
Fira Code: https://github.com/tonsky/FiraCode (Free)