Eloquent JavaScript (chapter 0-2)

Introduction

It is up to you to make the necessary effort. When you are struggling to follow the book, do not jump to any conclusions about your own capabilities. You are fine—you just need to keep at it. Take a break, reread some material, and make sure you read and understand the example programs and exercises. Learning is hard work, but everything you learn is yours and will make subsequent learning easier.

The art of programming is the skill of controlling complexity.

A sense of what a good program looks like is developed in practice, not learned from a list of rules.

Values, Types, and Operators

basic data type

• number
• string

`(backtick反引号)
escaping 转义 \n
concatenate: “con” + “cat” + “e” + “nate”
template literals: half of 100 is **${**100 / 2**}** ${xxx}内的xxx会计算值
Unary operators(一元运算符)：typeOf “x”

• Boolean
• null
• undefined
• symbol

short-circuit evaluation短路逻辑

• a || b : a为真则返回a,否则返回b
• a && b : a为假则返回a,否则返回b

  Program Structure

  A fragment of code that produces a value is called an expression.
  If an expression corresponds to a sentence fragment, a JavaScript statement corresponds to a full sentence.
  A program is a list of statements.

The simplest kind of statement is an expression with a semicolon after it. 1;
a binding, or variable:

let caught = 5 * 5;

You should imagine bindings as tentacles, rather than boxes. They do not contain values; they grasp them—two bindings can refer to the same value.

The collection of bindings and their values that exist at a given time is called the environment.

Executing a function is called invoking, calling, or applying it

console.log

let x = 30;
console.log("the value of x is", x);
// → the value of x is 30

When a function produces a value, it is said to return that value.

Math.max(2,1,3,5,9)
// 9
Math.min(2,1,3,5,9)
// 1

braces ({ and })
The braces can be used to group any number of statements into a single statement, called a block.

indent 2 spaces

exercises

1. 打出三角形阵列

for (let i = "#"; i.length < 8; i += "#")
  console.log(i)

2. FizzBuzz

for (let i = 1; i <= 100; i++) {
  let output = ''
  if (i % 3 === 0) output += "Fizz"
  if (i % 5 === 0) output += "Buzz"
  console.log(output || i)
}

3. 象棋盘

let size = 8
for (let i = 0; i < size; i++){
  let output = ''
  for(let j = 0; j < size; j++) {
    if ((i + j) % 2 === 0) output += " "
    else output += "#"
  }
  console.log(output)
}