4.-callback-hell

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"use strict";

function asyncSqrt(value, callback) {
    console.log('START execution with value =', value);
    setTimeout(function () {
        callback(value, value * value);
    }, 0 | Math.random() * 100);
}

asyncSqrt(0, function (value, result) {
    console.log('END execution with value =', value, 'and result =', result);
    asyncSqrt(1, function (value, result) {
        console.log('END execution with value =', value, 'and result =', result);
        asyncSqrt(2, function (value, result) {
            console.log('END execution with value =', value, 'and result =', result);
            asyncSqrt(3, function (value, result) {
                console.log('END execution with value =', value, 'and result =', result);
                asyncSqrt(4, function (value, result) {
                    console.log('END execution with value =', value, 'and result =', result);
                    asyncSqrt(5, function (value, result) {
                        console.log('END execution with value =', value, 'and result =', result);
                        asyncSqrt(6, function (value, result) {
                            console.log('END execution with value =', value, 'and result =', result);
                            asyncSqrt(7, function (value, result) {
                                console.log('END execution with value =', value, 'and result =', result);
                                asyncSqrt(8, function (value, result) {
                                    console.log('END execution with value =', value, 'and result =', result);
                                    asyncSqrt(9, function (value, result) {
                                        console.log('END execution with value =', value, 'and result =', result);
                                        console.log('COMPLETED');
                                    });
                                });
                            });
                        });
                    });
                });
            });
        });
    });
});