function mergeParams(target, source) {
    Object.keys(source).forEach(function (key) {
        if (!(key in target)) {
            target[key] = [];
        }
        target[key] = target[key].concat(source[key]);
    });
}
function mergeParams(target, source) {
    Object.keys(source).forEach(function (key) {
        if (!(key in target)) {
            target[key] = [];
        }
        target[key] = target[key].concat(source[key]);
    });
}
function mergeParams ( target , source ) { Object . keys ( source ) . forEach ( function ( key ) { if ( ! ( key in target ) ) { target [ key ] = [ ] ; } target [ key ] = target [ key ] . concat ( source [ key ] ) ; } ) ; }
Merges params from `source` into `target` (mutating `target`).

@param {!Object<string, !Array<string>>} target
@param {!Object<string, !Array<string>>} source
Merges params from source into target ( mutating target ) .