（一）小案例银行家应用程序-介绍

案例示例如下所示：

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登录之后就会出现下面所示：
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项目案例流程图如下
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● 首先我们建立四个账号对象，用于登录

const account1 = {owner: 'ItShare',movements: [200, 450, -400, 3000, -650, -130, 70, 1300],interestRate: 1.2, // %pin: 1111,
};const account2 = {owner: 'Jessica Davis',movements: [5000, 3400, -150, -790, -3210, -1000, 8500, -30],interestRate: 1.5,pin: 2222,
};const account3 = {owner: 'Steven Thomas Williams',movements: [200, -200, 340, -300, -20, 50, 400, -460],interestRate: 0.7,pin: 3333,
};const account4 = {owner: 'Sarah Smith',movements: [430, 1000, 700, 50, 90],interestRate: 1,pin: 4444,
};

● 上述我们模拟数据都是来自与Web API，再将四个账户数据存储到一个数组中

const accounts = [account1, account2, account3, account4];

● 其中HTML代码如下

<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta http-equiv="X-UA-Compatible" content="ie=edge" /><link rel="shortcut icon" type="image/png" href="icon.png" /><linkhref="https://fonts.googleapis.com/css?family=Poppins:400,500,600&display=swap"rel="stylesheet"/><link rel="stylesheet" href="style.css" /><title>Bankist</title></head><body><!-- TOP NAVIGATION --><nav><p class="welcome">Log in to get started</p><img src="logo.png" alt="Logo" class="logo" /><form class="login"><inputtype="text"placeholder="user"class="login__input login__input--user"/><!-- In practice, use type="password" --><inputtype="text"placeholder="PIN"maxlength="4"class="login__input login__input--pin"/><button class="login__btn">&rarr;</button></form></nav><main class="app"><!-- BALANCE --><div class="balance"><div><p class="balance__label">Current balance</p><p class="balance__date">As of <span class="date">05/03/2037</span></p></div><p class="balance__value">0000€</p></div><!-- MOVEMENTS --><div class="movements"><div class="movements__row"><div class="movements__type movements__type--deposit">2 deposit</div><div class="movements__date">3 days ago</div><div class="movements__value">4 000€</div></div><div class="movements__row"><div class="movements__type movements__type--withdrawal">1 withdrawal</div><div class="movements__date">24/01/2037</div><div class="movements__value">-378€</div></div></div><!-- SUMMARY --><div class="summary"><p class="summary__label">In</p><p class="summary__value summary__value--in">0000€</p><p class="summary__label">Out</p><p class="summary__value summary__value--out">0000€</p><p class="summary__label">Interest</p><p class="summary__value summary__value--interest">0000€</p><button class="btn--sort">&downarrow; SORT</button></div><!-- OPERATION: TRANSFERS --><div class="operation operation--transfer"><h2>Transfer money</h2><form class="form form--transfer"><input type="text" class="form__input form__input--to" /><input type="number" class="form__input form__input--amount" /><button class="form__btn form__btn--transfer">&rarr;</button><label class="form__label">Transfer to</label><label class="form__label">Amount</label></form></div><!-- OPERATION: LOAN --><div class="operation operation--loan"><h2>Request loan</h2><form class="form form--loan"><input type="number" class="form__input form__input--loan-amount" /><button class="form__btn form__btn--loan">&rarr;</button><label class="form__label form__label--loan">Amount</label></form></div><!-- OPERATION: CLOSE --><div class="operation operation--close"><h2>Close account</h2><form class="form form--close"><input type="text" class="form__input form__input--user" /><inputtype="password"maxlength="6"class="form__input form__input--pin"/><button class="form__btn form__btn--close">&rarr;</button><label class="form__label">Confirm user</label><label class="form__label">Confirm PIN</label></form></div><!-- LOGOUT TIMER --><p class="logout-timer">You will be logged out in <span class="timer">05:00</span></p></main><!-- <footer>&copy; by Jonas Schmedtmann. Don't claim as your own :)</footer> --><script src="script.js"></script></body>
</html>

● CSS代码如下
/*

 * Use this CSS to learn some intersting techniques,* in case you're wondering how I built the UI.* Have fun! 😁*/* {margin: 0;padding: 0;box-sizing: inherit;
}html {font-size: 62.5%;box-sizing: border-box;
}body {font-family: "Poppins", sans-serif;color: #444;background-color: #f3f3f3;height: 100vh;padding: 2rem;
}nav {display: flex;justify-content: space-between;align-items: center;padding: 0 2rem;
}.welcome {font-size: 1.9rem;font-weight: 500;
}.logo {height: 5.25rem;
}.login {display: flex;
}.login__input {border: none;padding: 0.5rem 2rem;font-size: 1.6rem;font-family: inherit;text-align: center;width: 12rem;border-radius: 10rem;margin-right: 1rem;color: inherit;border: 1px solid #fff;transition: all 0.3s;
}.login__input:focus {outline: none;border: 1px solid #ccc;
}.login__input::placeholder {color: #bbb;
}.login__btn {border: none;background: none;font-size: 2.2rem;color: inherit;cursor: pointer;transition: all 0.3s;
}.login__btn:hover,
.login__btn:focus,
.btn--sort:hover,
.btn--sort:focus {outline: none;color: #777;
}/* MAIN */
.app {position: relative;max-width: 100rem;margin: 4rem auto;display: grid;grid-template-columns: 4fr 3fr;grid-template-rows: auto repeat(3, 15rem) auto;gap: 2rem;/* NOTE This creates the fade in/out anumation */opacity: 0;transition: all 1s;
}.balance {grid-column: 1 / span 2;display: flex;align-items: flex-end;justify-content: space-between;margin-bottom: 2rem;
}.balance__label {font-size: 2.2rem;font-weight: 500;margin-bottom: -0.2rem;
}.balance__date {font-size: 1.4rem;color: #888;
}.balance__value {font-size: 4.5rem;font-weight: 400;
}/* MOVEMENTS */
.movements {grid-row: 2 / span 3;background-color: #fff;border-radius: 1rem;overflow: scroll;
}.movements__row {padding: 2.25rem 4rem;display: flex;align-items: center;border-bottom: 1px solid #eee;
}.movements__type {font-size: 1.1rem;text-transform: uppercase;font-weight: 500;color: #fff;padding: 0.1rem 1rem;border-radius: 10rem;margin-right: 2rem;
}.movements__date {font-size: 1.1rem;text-transform: uppercase;font-weight: 500;color: #666;
}.movements__type--deposit {background-image: linear-gradient(to top left, #39b385, #9be15d);
}.movements__type--withdrawal {background-image: linear-gradient(to top left, #e52a5a, #ff585f);
}.movements__value {font-size: 1.7rem;margin-left: auto;
}/* SUMMARY */
.summary {grid-row: 5 / 6;display: flex;align-items: baseline;padding: 0 0.3rem;margin-top: 1rem;
}.summary__label {font-size: 1.2rem;font-weight: 500;text-transform: uppercase;margin-right: 0.8rem;
}.summary__value {font-size: 2.2rem;margin-right: 2.5rem;
}.summary__value--in,
.summary__value--interest {color: #66c873;
}.summary__value--out {color: #f5465d;
}.btn--sort {margin-left: auto;border: none;background: none;font-size: 1.3rem;font-weight: 500;cursor: pointer;
}/* OPERATIONS */
.operation {border-radius: 1rem;padding: 3rem 4rem;color: #333;
}.operation--transfer {background-image: linear-gradient(to top left, #ffb003, #ffcb03);
}.operation--loan {background-image: linear-gradient(to top left, #39b385, #9be15d);
}.operation--close {background-image: linear-gradient(to top left, #e52a5a, #ff585f);
}h2 {margin-bottom: 1.5rem;font-size: 1.7rem;font-weight: 600;color: #333;
}.form {display: grid;grid-template-columns: 2.5fr 2.5fr 1fr;grid-template-rows: auto auto;gap: 0.4rem 1rem;
}/* Exceptions for interst */
.form.form--loan {grid-template-columns: 2.5fr 1fr 2.5fr;
}
.form__label--loan {grid-row: 2;
}
/* End exceptions */.form__input {width: 100%;border: none;background-color: rgba(255, 255, 255, 0.4);font-family: inherit;font-size: 1.5rem;text-align: center;color: #333;padding: 0.3rem 1rem;border-radius: 0.7rem;transition: all 0.3s;
}.form__input:focus {outline: none;background-color: rgba(255, 255, 255, 0.6);
}.form__label {font-size: 1.3rem;text-align: center;
}.form__btn {border: none;border-radius: 0.7rem;font-size: 1.8rem;background-color: #fff;cursor: pointer;transition: all 0.3s;
}.form__btn:focus {outline: none;background-color: rgba(255, 255, 255, 0.8);
}.logout-timer {padding: 0 0.3rem;margin-top: 1.9rem;text-align: right;font-size: 1.25rem;
}.timer {font-weight: 600;
}

● 在此之前，我们要将我们所有需要的元素存储到变量中，方便我们后续使用

const labelWelcome = document.querySelector('.welcome');
const labelDate = document.querySelector('.date');
const labelBalance = document.querySelector('.balance__value');
const labelSumIn = document.querySelector('.summary__value--in');
const labelSumOut = document.querySelector('.summary__value--out');
const labelSumInterest = document.querySelector('.summary__value--interest');
const labelTimer = document.querySelector('.timer');const containerApp = document.querySelector('.app');
const containerMovements = document.querySelector('.movements');const btnLogin = document.querySelector('.login__btn');
const btnTransfer = document.querySelector('.form__btn--transfer');
const btnLoan = document.querySelector('.form__btn--loan');
const btnClose = document.querySelector('.form__btn--close');
const btnSort = document.querySelector('.btn--sort');const inputLoginUsername = document.querySelector('.login__input--user');
const inputLoginPin = document.querySelector('.login__input--pin');
const inputTransferTo = document.querySelector('.form__input--to');
const inputTransferAmount = document.querySelector('.form__input--amount');
const inputLoanAmount = document.querySelector('.form__input--loan-amount');
const inputCloseUsername = document.querySelector('.form__input--user');
const inputClosePin = document.querySelector('.form__input--pin');