JavaScript 中的条件分支：`if`、`else` 和 `?`

if (condition) {  // code to execute if condition is true}

let age = 18;if (age >= 18) {  console.log("you are an adult.");}

let value = 0;if (value) {  console.log("value is true.");} else {  console.log("value is false.");}// output: value is false.

if (condition) {  // code to execute if condition is true} else {  // code to execute if condition is false}

let age = 15;if (age >= 18) {  console.log("you are an adult.");} else {  console.log("you are a minor.");}

if (condition1) {  // code to execute if condition1 is true} else if (condition2) {  // code to execute if condition2 is true} else {  // code to execute if none of the conditions are true}

let score = 85;if (score >= 90) {  console.log("grade: a");} else if (score >= 80) {  console.log("grade: b");} else if (score >= 70) {  console.log("grade: c");} else {  console.log("grade: d");}

condition ? expriftrue : expriffalse;

let age = 20;let message = age >= 18 ? "you are an adult." : "you are a minor.";console.log(message);

let score = 85;let grade = score >= 90 ? "a" : score >= 80 ? "b" : score >= 70 ? "c" : "d";console.log("grade:", grade);

let userinput = "";let result = userinput ? userinput : "default value";console.log(result); // output: default value

let temperature = 25;if (temperature > 30) {  console.log("It's hot outside!");} else if (temperature > 20) {  console.log("It's warm outside.");} else if (temperature > 10) {  console.log("It's cool outside.");} else {  console.log("It's cold outside.");}let weather = temperature > 30 ? "hot" : temperature > 20 ? "warm" : temperature > 10 ? "cool" : "cold";console.log("The weather is:", weather);