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Boolean - MDN Web Docs Glossary: Definitions of Web-related terms 编辑

In computer science, a Boolean is a logical data type that can have only the values true or false. For example, in JavaScript, Boolean conditionals are often used to decide which sections of code to execute (such as in if statements) or repeat (such as in for loops).

Below is some JavaScript pseudocode (it's not truly executable code) demonstrating this concept.

/* JavaScript if statement */
if (boolean conditional) {
   // code to execute if the conditional is true
}

if (boolean conditional) {
  console.log("boolean conditional resolved to true");
} else {
  console.log("boolean conditional resolved to false");
}

/* JavaScript for loop */
for (control variable; boolean conditional; counter) {
  // code to execute repeatedly if the conditional is true
}

for (var i=0; i < 4; i++) {
  console.log("I print only when the boolean conditional is true");
}

The Boolean value is named after English mathematician George Boole, who pioneered the field of mathematical logic.