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Writing in es6 and using react 0.14.6 / react-router 2.0.0-rc5. I use this command to lookup the query params in my components:

this.props.location.query

It creates a hash of all available query params in the url.

Update:

For React-Router v4, see this answer. Basically, use this.props.location.search to get the query string and parse with the query-string package or URLSearchParams:

const params = new URLSearchParams(paramsString); 
const tags = params.get('tags');