Create this type of data structure in javascript

A quite straightforward approach would be transforming the Python lists to Javascript arrays, then access them as usual in the loop or reassign their values to local variables, if desired. Also make sure to convert the booleans to lowercase. The following example is compatible to pre-ES6 environments:

var data = [
    ['pale', 'ple', true],
    ['pales', 'pale', true],
    // ...
];

for (var i = 0; i < data.length; ++i)
{
    var row = data[i];
    var test_s1 = row[0];
    var test_s2 = row[1];
    var expected = row[2];
    // ...
}

If your target environment supports ES6, you could use this variant:

const data = [
    ['pale', 'ple', true],
    ['pales', 'pale', true],
    // ...
];

for (let row of data)
{
    let [test_s1, test_s2, expected] = row;
    // ...
}

Your python code in Javascript might look like this.

const data = [
    ['pale', 'ple', true],
    ['pales', 'pale', true],
    ['pale', 'bale', true],
    ['paleabc', 'pleabc', true],
    ['pale', 'ble', false],
    ['a', 'b', true],
    ['', 'd', true],
    ['d', 'de', true],
    ['pale', 'pale', true],
    ['pale', 'ple', true],
    ['ple', 'pale', true],
    ['pale', 'bale', true],
    ['pale', 'bake', false],
    ['pale', 'pse', false],
    ['ples', 'pales', true],
    ['pale', 'pas', false],
    ['pas', 'pale', false],
    ['pale', 'pkle', true],
    ['pkle', 'pable', false],
    ['pal', 'palks', false],
    ['palks', 'pal', false]
]

const printMyData = (data) => {
  data.forEach(arr => {
    console.log(arr[0] + ' ' + arr[1])
  })
}

printMyData(data)

You have to do some restructuring of your actual data first, and make sure your booleans are lowercase. printMyData is a function that accepts this data and forEach() of the arrays inside of it, logs the first and second element of it.

Use Javascript objects:

function makeTuple(s1, s2, expected) {
     return {
         s1: s1,
         s2: s2,
         expected: expected
     };
}

var data = [
    makeTuple('pale', 'ple', true),
    makeTuple('pales', 'pale', true),
    ...
];

for (var i = 0; i < data.length; i++) {
    var obj = data[i];
    console.log(obj.s1, obj.s2);
    // console.log(obj.expected);
}

Or you could simply use arrays:

var data = [
    ['pale', 'ple', true],
    ['pales', 'pale', true],
    ...
];

for (var i = 0; i < data.length; i++) {
    var obj = data[i];
    console.log(obj[0], obj[1]);
    // console.log(obj[2]);
}

If you do not want keys to be used, Simply create array of arrays:

var data = [['pale', 'ple', true], ['pale', 'ple', true], ['pale', 'ple', true]];