They are the same thing
Remember, that in JSON, the only allowed quote character is the double quotes.
Single quotes are more common
Dominant quote style
' - 76% of quotes
' - 92% of quotes
' - 73% of quotes
' - 97% of quotes
' - 78% of quotes
' - 58% of quotes
' - 52% of quotes
Use of quote character in popular projects.
The fact that front-end libraries have more double quotes than the other libraries might have to do with the presence of HTML fragments.
Looking at a few style guides reveals a mixed approach, about half recommending single quotes and other half double quotes.
gjslint (Google Closure Linter) favors ' single quotes
To avoid making a choice every time you're about to write a string, you should pick one style and stick with it. If your team is still making up your mind - pick single quotes, they are more common. In ES6, you'll have a third option to enclose strings - the `backtick` string.