const arr = [

  ["aaa 1", "bbb 1", "ccc 1", "ddd 1", ["aaa 2", "bbb 2", "ccc 2", "ddd 2"]],

  ["aaa 2", ["aaa 2", "bbb 2", "ccc 2", "ddd 2"], "bbb 2", "ccc 2", ["aaa 2", "bbb 2", "ccc 2", ["aaa 2", [["someth 2", ["someth 2", "ashhsjahjd 2", "hdsakhfkjsdk 2", "ddd 2"], "hdsakhfkjsdk 2", "ddd 2"], "ashhsjahjd 2", "hdsakhfkjsdk 2", "ddd 2"], "ccc 2", "ddd 2"]]],

  ["aaa 3", "bbb 3", "ccc 3", "ddd 3"],

  [["someth 2", "ashhsjahjd 2", "hdsakhfkjsdk 2", "ddd 2"], ["aaa 2", "someth 2", "ashhsjahjd 2", "hdsakhfkjsdk 2", "bbb 2", "ccc 2", "ddd 2"], "ccc 4", [["someth 2", ["someth 2", "ashhsjahjd 2", "hdsakhfkjsdk 2", "ddd 2"], "hdsakhfkjsdk 2", "ddd 2"], "bbb 2", "ccc 2", ["someth 2", "ashhsjahjd 2", ["someth 2", "ashhsjahjd 2", "hdsakhfkjsdk 2", "ddd 2"], "ddd 2"]]]

];

​

const flattenArr = (arr) => {

​

    const flatArray = [];

    const parseArray = (arr) => {

        arr.forEach(item => Array.isArray(item) ? parseArray(item) : flatArray.push(item))

    }

    parseArray(arr)

​

    return flatArray

}

​

console.log(flattenArr(arr));