Duffer Derek

/**
 * Use invariant() to assert state which your program assumes to be true.
 *
 * Provide sprintf-style format (only %s is supported) and arguments
 * to provide information about what broke and what you were
 * expecting.
 *
 * The invariant message will be stripped in production, but the invariant
 * will remain to ensure logic does not differ in production.
 */ export function invariant(condition, format, ...args) {
    if (isProduction()) {
        if (format === undefined) {
            throw new Error('invariant requires an error message argument');
        }
    }
    if (!condition) {
        let error;
        if (format === undefined) {
            error = new Error('Minified exception occurred; use the non-minified dev environment ' + 'for the full error message and additional helpful warnings.');
        } else {
            let argIndex = 0;
            error = new Error(format.replace(/%s/g, function() {
                return args[argIndex++];
            }));
            error.name = 'Invariant Violation';
        }
        error.framesToPop = 1 // we don't care about invariant's own frame
        ;
        throw error;
    }
}
function isProduction() {
    return typeof process !== 'undefined' && process.env['NODE_ENV'] === 'production';
}

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