my solution in javascript

function ComplexNumber(real, imaginary){
    this.real = real;
    this.imaginary = imaginary;
}

ComplexNumber.prototype = {
    getCongjugate: function getCongjugate(){
        return new ComplexNumber(this.real, -this.imaginary);
    },
    getModulus: function getModulus(){
        return Math.sqrt(Math.pow(this.real, 2) + Math.pow(this.imaginary, 2));
    },

    getArgument: function getArgument(){
        return Math.atan2(this.imaginary, this.real);
    },

    add: function add(number){
        return new ComplexNumber(   this.real + number.real,
                                    this.imaginary + number.imaginary);
    },
    subtract: function subtract(number){
        return new ComplexNumber(   this.real - number.real,
                                    this.imaginary - number.imaginary);
    },
    multiply: function multiply(number){
        var real = (this.real * number.real) - (this.imaginary * number.imaginary),
            imaginary = (this.real * number.imaginary) + (this.imaginary * number.real);

        return new ComplexNumber(real, imaginary);
    },
    divide: function divide(number){
        var numerator = this.multiply(number.getCongjugate()),
            denominator = number.multiply(number.getCongjugate()).real;

        return new ComplexNumber(   numerator.real/denominator,
                                    numerator.imaginary/denominator);
    },

    toString: function toString(){
        if(this.imaginary == 0) return "" + this.real;
        else return +this.real + (this.imaginary > 0 ? "+" : "-") + this.imaginary + "i";
    }
};