@textlint/kernel/src/util/invariant.ts

textlint kernel is core logic by pure JavaScript.

/**
 * Test if condition is truthy.
 * @param {any} expression to be evaluated
 * @param {string} error message to be shown
 * @returns {void}
 * @throws
 */
export function invariant(condition: any, message?: string): asserts condition {
    if (!condition) throw new Error(message);
}