dist/vue-resource.esm.js
function header (request) {

    var headers = assign({}, Http.headers.common,
        !request.crossOrigin ? Http.headers.custom : {},
        Http.headers[toLower(request.method)]
    );

    each(headers, function (value, name) {
        if (!request.headers.has(name)) {
            request.headers.set(name, value);
        }
    });

}
function header (request) {

    var headers = assign({}, Http.headers.common,
        !request.crossOrigin ? Http.headers.custom : {},
        Http.headers[toLower(request.method)]
    );

    each(headers, function (value, name) {
        if (!request.headers.has(name)) {
            request.headers.set(name, value);
        }
    });

}
function header ( request ) { var headers = assign ( { } , Http . headers . common , ! request . crossOrigin ? Http . headers . custom : { } , Http . headers [ toLower ( request . method ) ] ) ; each ( headers , function ( value , name ) { if ( ! request . headers . has ( name ) ) { request . headers . set ( name , value ) ; } } ) ; }
Header Interceptor.
Header Interceptor .