07. Area of Figures

function areaOfFigures(input) {
    figure = input[0];
    let sum = 0.0;

    if (figure === "circle") {
        let radius = Number(input[1]);
        sum = radius * radius * Math.PI;  // Или: sum = radius ** 2 * Math.PI;
    } else if (figure === "triangle") {
        let lenght = Number(input[1]);
        let hight = Number(input[2]);
        sum = lenght * hight / 2;
    } else if (figure === "square") {
        let side = Number(input[1]);
        sum = side * side;               // Или: sum = side ** 2
    } else {
        let sideA = Number(input[1]);
        let sideB = Number(input[2]);
        sum = sideA * sideB;
    }
    console.log(sum.toFixed(3));
}

РЕШЕНИЕ С РЕЧНИК:

function areaOfFigures(input) {
    figure = input[0];
    a = Number(input[1]);
    b = Number(input[2]);

    formulas = {
        'square': a ** 2,
        'circle': a ** 2 * Math.PI,
        'triangle': a * b / 2,
        'rectangle': a * b
    };
    console.log(`${(formulas[figure]).toFixed(3)}`);
}

Тарикатско решение с тернарен оператор:

function areaOfFigures(input) {

    if (input[0] == 'circle' || input[0] == 'square') {
        console.log((Number(input[1]) ** 2 * (input[0] === 'circle' ? Math.PI : 1)).toFixed(3));
    } else if (input[0] == 'triangle' || input[0] == 'rectangle') {
        console.log((Number(input[1]) * Number(input[2]) / (input[0] === 'triangle' ? 2 : 1)).toFixed(3));
    }
}