// set indent level e.g. 4 spaces

let indent = " ".repeat(4),

    indentLevel = 0,

    codeBlock = document.querySelector('pre code');

​

codeBlock.innerHTML = "function myFunc () {\n";

​

++indentLevel;

codeBlock.innerHTML += indent + "if (something) {\n";

​

++indentLevel;

codeBlock.innerHTML += indent.repeat(indentLevel) + "return true;\n";

​

--indentLevel;

codeBlock.innerHTML += indent.repeat(indentLevel) + "}\n";

​

--indentLevel;

codeBlock.innerHTML += indent.repeat(indentLevel) + "}\n";